Telephones are a crucial part of modern living while at home, but taking them on the road when travelling can get expensive. Hotels often overcharge for trunk calls from room telephones, while mobile providers charge inflated "roaming" fees if calls made while abroad are billed through your home provider.

By contrast, a high-speed Internet connection can be used to make calls to landlines in most industrialised nations for a penny or two a minute; calls to other Internet telephony users on the same service are often free.

Get on-line

Where you have full access to the Internet at a reasonable speed and price, making phone calls over the Internet is the cheapest option.

Free calls are possible if both parties have Internet access and are running the same or compatible software; many laptops, smartphones and tablets now include a small built-in camera (webcam) for video calls. Softphone clients for many webcam servers (such as Skype, FaceTime or Viber) are free to download or come included in your device.

Calls where one party is using a conventional telephone and the other is using an Internet connection (such as a Wi-Fi hotspot) are not free, but are far less expensive than conventional telephony. A call to a landline anywhere from London to Los Angeles from the broadband Internet costs as little as a penny a minute, as the voice service provider (VSP) doesn't have to transport the call to those faraway places – the Internet already does that. The VSP merely finds a least-expensive gateway to convert the call back to landline telephony at destination.

When carrying a portable device (laptop, smartphone or tablet) to a location which provides access to a Wi-Fi hotspot, access to inexpensive Internet telephony merely requires installation of (usually free) software and signup to a voice service provider (VSP). Be sure to test your configuration before departing.

A headset will give better sound quality than the built-in speakers if using a PC or tablet; smaller devices (iPhone, iPod Touch, Blackberry, Android handset) are suited directly for use as telephone handsets, giving the look and feel of mobile telephony with no need for any external hardware. The quality of the actual telephone calls, in any case, will remain at the mercy of the underlying Internet connection. If connection speed is sporadic and unreliable, the audio will contain annoying dropouts; if the connection is consistently fast (both outbound and inbound) an Internet telephone will work well.

Some PC applications suppose you have a good connection and by default use a codec (coder-decoder) which optimizes voice quality at the expense of bandwidth. With a codec optimized for compression, a data rate well under the 56 kbps of a landline connection may suffice; without compression, one voice call plus packet overhead uses about 80kbps and needs this data rate consistently. For some connections you may want to allow much more lag than the default, as delayed packets will otherwise be discarded.

Fax

Internet telephony behaves poorly if used as a virtual "telephone line" to serve any device that contains a dial-up modem. A VoIP connection is virtual and adequate to transmit voice, but plugging in a fax machine (or the few other devices that still contain otherwise-obsolete dial-up modems) isn't going to work because Internet packets will often be dropped or delayed during a call, causing errors and disconnections. In theory, there is a T.38 standard where analogue telephone adapter boxes can demodulate the fax tones, extract the original digital data and send that instead. In practice, T.38 support among upstream providers remains rare to non-existent and T.38 is only useful if the provider supports it.

The usual workaround is to choose a voice provider which provides a fax-to-Internet gateway; an inbound fax is converted to a PDF file as soon as it arrives from the public switched telephone network and either e-mailed or made available for web download; an outbound fax is uploaded in a similar manner. No fax tones go through the fragile real-time VoIP connection, so the system is reliable. Eventually, the business community will acknowledge that (as a low-quality computer-scanned image sent on a slow dial-up modem) a fax is no more a "reliable original document" than the same piece of paper scanned to PDF and attached to a standard e-mail message. Hôteliers will be among the last to accept this (as the hotel's fax machine connected to an old-fashioned landline is an "incidental expense" for which business travellers were willing to pay per page), followed by solicitors as the last to change (lawyers love paper and a printed fax somehow looked more official). In the meantime, just hand out the "special fax number" issued by your VoIP provider's gateway and no one need know these missives merely land in the same "in" box as the rest of the e-mail and the spam.

Blocks and obstacles

Some publicly available networks can block VOIP, many are simply too slow, and in some countries, Internet telephony is blocked entirely to protect overpriced national phone monopolies. Public hotspots vary widely in quality; some may provide access to the full Internet, others might provide access to just the Web (which is one Internet application among many) or a limited number of services while blocking everything else. Some may only enable a connection after a user opens a webpage and "agrees" to a long list of incomprehensible conditions and legalese. These issues are independent of the speed of the underlying connection.

VOIP is a good way to maintain contact with friends and family while travelling, who will tolerate the occasional drop-out. It may not be the best way to maintain a connection with important business contacts. In some destinations, one may rent a computer with Skype from a local Internet store.

Until recently, Etisalat, the state-owned telecommunications provider of the United Arab Emirates allowed connections to the Skype network, blocking only the company website to prevent users from adding credit to their accounts to make PSTN calls. The restrictions were later reinforced by blocking access to the Skype network entirely. However, Skype is still accessible from some hotels that provide access through 'TheWayOut' Wi-Fi service.

Some providers may block calls placed from IP addresses in various foreign lands, if those foreign countries are a source of fraudulent Internet telephone calls or abnormal patterns of usage. A few providers block calls to certain high-priced destinations, unless they receive a verifiable request from the subscriber to unlock them. The same approach to flagging unusual usage patterns occurs with other on-line services (so repeated attempts to log in from Moscow to a Google account which belongs to a North American user might be flagged as questionable); check with your provider before departure.

A virtual private network (VPN) will allow you to connect to your own home-country office and circumvent many of these issues (you can even appear to still be at your desk when you're actually travelling the world on business), although a few particularly dictatorial nations will deny you access to VPN or even to the Internet in general.

Equipment and applications

There are various ways to get on-line to make inexpensive voice calls; these fall into two main categories:

• hardware such as self-contained Internet telephones or adapters to plug wireline handsets into the network
• softphones, application software which turns a smartphone, tablet or PC into an Internet telephone

Dedicated devices

Various devices are promoted for home or office use:

• Analogue telephone adapters (which plug into a standard landline handset and a wired Internet connection). Common for residential use, and usually will still work if taken to another city and plugged into the Internet, but with two boxes (a phone and an adapter) too bulky to be easily portable.
• VoIP office telephones, which are self-contained and just need to plug into the Internet. One piece, but still bulky for travellers.
• Various add-ons for laptop or desktop PC's which appear to be wired or wireless telephone handsets, telephone line jacks or headsets. Most are based on using a PC software application (smartphone) to do most of the work, while the hardware merely operates as a computer sound card.

While certainly capable of providing the functionality of a standard desk telephone, in many cases without the need for a computer, these are intended for fixed installation (such as home or office) as they are awkward to carry.

Android softphones

There are various free applications (SipDroid, Vimphone, CSipSimple) which can be used to make telephone calls from Android-based smartphones. As these use the handset's wi-fi connection, there is no need for a cellular/mobile telephone subscription. With these apps, a SIP provider is needed to reach standard telephones; costs start at $1/month (per incoming number) plus $0.01/minute (incoming and outbound, local or long distance, based on voip.ms).

As with PC's, there are instant messenger applications which can communicate with other Internet users on the same service for free.

As prepaid mobile vendors are flooding the market with under-$100 Android devices, the costly single-purpose "cordless wi-fi Internet phone" handsets are becoming rare. It's actually cheaper to buy the general-purpose Android and install a free app to use it as a cordless VoIP phone.

The form factor of a typical Android, Blackberry smartphone or iPod looks and feels like a telephone handset, making the platforms ideal for running Internet calls over wi-fi. No need for a separate microphone and headset, the whole package is one inexpensive pocket-sized device which typically also provides an e-mail client, camera, media player and travel alarm clock.

iPhone/iPod apps

Capabilities are similar to those of Android devices, although specific applications to make SIP calls will vary (Acrobits, Fring, Linphone, Media5-fone, NetDial Sip Phone and Zoiper all exist on both platforms). It is possible to make calls from the iPod Touch, which is not a telephone but which supports wi-fi and has a front camera for webcam-style instant messenger calls. Apple's proprietary messenger, FaceTime, is supported on iPod and iPhone.

Laptop and PC

Most of the standard instant messenger and webcam applications (such as Google Voice, Yahoo or Skype) originated on PC's, although some now also have iOS or Android versions. When using a tablet, laptop or PC it may be desirable to add a wired headset or a wireless Bluetooth headset; the audio otherwise will be speakerphone quality at best.

Various SIP-compatible softphones (such as Ekiga) may be used to call from a computer to the telephone network through a SIP provider. Some messenger apps can be used to call telephones for a fee, which is usually higher than the cheapest unbundled SIP voice-over-IP services.

Internet phone companies

Because calls are routed over the Internet, you do not need to use a phone company located where you live or where you travel. There is also no requirement that you obtain a local number from the community in which you live; you can obtain a satellite Internet connection in the wilds of Chicken, Alaska and select a number which claims you're in sunny Arizona. Often, you have to buy a global number separately that allows PSTN phones to call you. Where the number is from makes a difference for people calling you.

SIP Phone companies

There are literally thousands of VOIP companies. It is best to pick a company which has connections either in the country you are calling from or calling to, to avoid unnecessary international hops.

Many (but not all) of these providers will allow free calls over the Internet to other subscribers on the same server, as these internal calls never reach the public switched telephone network (PSTN).

UK and Europe

• Betamax GmbH (VoIP Buster, VoipCheap, VoipDiscount, VoIP Stunt) Germany. Various plans under different branding offer "free calls" to a few dozen countries (in Europe or scattered worldwide, landline) for a few months after purchase of prepaid credits. The Betamax products appear to be limited by IP address, so 'roaming' may not work well. Some brands offer voip in numbers in European countries.
• Localphone VoIP Services UK-based. Free Localphone–Localphone calls, cheap calls over PSTN.
• SipDiscount Luxembourg. Free 1 min trial calls to many countries.
• SkySIPtel Broadband Phone. Spain. Cheap VoIP SIP Services

USA

• AT&T CallVantage
• IConnectHere. New Jersey. Prepaid from $10.00.
• IPKall, nominally-free incoming calls using numbers in rural Washington (state) area code +1 360.
• Lucky Telecom Corp. A-Z VoIP termination and proper termination services, primarily for resellers.
• Vitelity, Denver. Unbundled prepaid SIP voice with local North American numbers. Internet fax gateway (send and receive). Fax numbers are US local (various cities) or North American +1-800/888 tollfree.
• Vonage Nominally SIP, but known to lock you out of your device settings.
• 7AAA VoIP Termination VoIP termination in SIP

Canada

• Les.net. Prepaid SIP, Canada/US inbound (local numbers in most cities), North America tollfree numbers. From $2/month and 1.5 cents/minute, with a Winnipeg (+1-204-666) incoming number included. Can receive FAX (gated to e-mail) but not send FAX.
• VBuzzer, Toronto/York Region. Prepaid SIP, inbound Canada/US numbers, two cents/minute. Fax in/out is possible if using their supplied Windows XP softphone.
• VoIP.ms Montréal. Prepaid SIP, Canada/US local (most cities $1/month + $0.01/minute) and tollfree inbound numbers, international numbers, one cent/minute outbound to most western landlines, no minimum charge. Multiple points of presence in US, Canada, UK. Fax support with North American numbers only.
• MyOwntelco Montréal. Prepaid SIP, North America coverage and access number in more than 3000 cities, local inbound numbers $7/month (most cities), 0.6 cents/minute calls to Canada, US/ Western Europe Landline from 1 cent, Fax to email, International DID, Sip client for smartphone.

Non-SIP phone companies

• Dialpad
• Net2Phone
• Skype. Free computer-to-computer calls: pay a fee for Skype-Out service to call anyone else or pay a fee for Skype-In service to get a phone number where people can call your computer. Skype claims to be secure by using strong encryption to protect your messages, but some experts have been scathingly sceptical about those claims.
• United World Telecom

Callback

These websites call you on your homeline and the person you want to call, using normal phones.

• Peterzahlt.de With this German website it is possible to make free calls from/to Germany for 10 min for non-members and 30 min for members
• VoIP Internet Service Callback free with registration.
• Spaxtel.com Crystal clear international calls with iPhone, Android and Blackberry apps available.
• UWT Callback Service.

Direct inward system access

Direct inward system access (DISA) is a feature deployed by some Asterisk PBX-based providers, such as Swiftvox (voip.ms). It functions much like a calling card service; dial your own number using a normal phone, enter a code, then get a dial tone from your voice-over-IP provider's private branch exchange to call back out inexpensively using Internet telephony. It's more expensive than calling with a softphone app from a wi-fi hotspot (as this incurs the cost of both an inbound and an outbound call) but can be a viable alternative to purchasing prepaid calling cards.

A similar concept is a "calling card number" provided by a voice-over-IP carrier as part of the same package (or on the same bill) as Internet telephone service. These can allow travellers to avoid the short expiry dates and many hidden fees on prepaid cards in local convenience stores, but be sure to check that you (or your carrier) have a local access number in the places you plan to visit.

Messenger applications

Yahoo Messenger (YM) allows users of selected countries to call any phone after topping-up (via credit card) starting at $10.00. As with Skype-to-Skype calls, YM calls to another active YM user on the Internet are free of charge.

Google Voice may be used to make inexpensive calls and can provide a local number in the United States of America.

Apple's FaceTime allows free video calls between users of MacBook, iPhone or iPad devices; the software is pre-installed on the latest versions of the iPhone and iPad. Unlike Skype's video calling, FaceTime is not available for non-Apple devices (such as Androids or Windows/Linux PC's).

Other Internet services

Some Internet phone companies like Musimi will forward voicemail messages as email attachments so you can listen to them at Internet cafés when travelling. This is also part of the package at some of the VoIP carriers (along with the standard options to forward to a regular telephone number or an Internet device).

• HolidayPhone anti-roaming SIM resells a foreign SIM card for your destination, and forward your calls made to your ordinary UK number over Internet to your foreign SIM card. That way, you stay reachable and can receive free calls on your ordinary number while abroad, and can still call at local rates.
• Lonely planets Ekit even allows people to leave messages on your voicemail for free using a toll-free number and you can then retrieve them from the Ekit home page or pay to listen to them from a phone.