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Mobile phone service while traveling is a convenient way to contact local businesses or acquaintances, find travel partners when separated, or keep handy in case of emergency. However, differing technology standards and the range of prices between options can make it difficult to select the right option for your travels.

There are four main ways to use a mobile phone when traveling abroad:

• Take a phone from home and simply use it abroad. Known as international roaming, you will be billed by your service provider for usage abroad. This is both the most convenient and most expensive choice.
• Take a phone from home and purchase a SIM card at your destination, allowing your phone to work with the foreign mobile service provider. Without needing to purchase a phone abroad, this can be a cheap option for some. Technical aspects can complicate the compatibility of phones with different mobile networks.
• Purchase both a phone and service from a mobile service provider. This ensures compatibility with a mobile phone network and for a basic phone can be fairly inexpensive. Some countries allow service providers to "lock" phones to their networks and combined with different technical aspects between networks, the purchased phone may not operate with other networks. This is a convenient option that can be cheaper than roaming.
• Rent a mobile phone. Prices can be high—comparable to roaming costs or purchasing both a phone & service.

With smartphones, it is possible to use messaging apps, video conferencing services/apps, and voice over internet protocol (VoIP) apps when connected to WiFi as a convenient substitute to mobile phone service. Since this does not involve using mobile phone networks, it is not covered in this article.

Roaming

Roaming is the most convenient way to use a mobile phone abroad, but has a few drawbacks. Many mobile service providers have agreements with providers in other countries to allow their customers to use those foreign networks at fixed prices. Simply take the phone you own and pay for service at home and use it while abroad. The phone uses the foreign network, with charges passed on to your mobile service provider, who adds those charges to your typical bill (or subtracts from your available prepaid balance). Both incoming and outgoing calls will be charged, even if this is not a normal practice for your service provider. A call between you and another phone within the country you are roaming in may be considered an international call. You may also be charged for incoming called that aren't answered, calls directed to voicemail, and calls made to voicemail.

It's worth contacting your service provider before leaving home to learn of roaming rates in the countries you plan to travel, as rates can vary significantly. Service providers may not allow roaming for all customers/accounts by default and customers need to authorize international roaming on their phone/account; some service providers charge a fee to allow international roaming on an account in addition to charges accrued for actual use while roaming. It may also be possible to permit international roaming for just voice and prevent international roaming for data.

Charges for data use (ie. internet) while abroad can be astronomical. Smartphones use data on a mobile phone network for tasks that a traveler may not be aware, such as checking for and downloading email or downloading voicemail and apps that update in the background, like apps that display current weather or check for and display news stories. In the major smartphone operating systems, it is possible to disable data use when roaming through the settings (you can still connect to WiFi to allow data use). Likewise, it is also possible to enable/disable voice roaming, which is useful if you only want to permit roaming in certain countries or a certain times but want to leave the phone on with WiFi enabled (as the more well-known "airplane mode" disables all connections).

Technical considerations

It is important to understand that underlying the communication between mobile phones and the mobile phone towers there are several different standards and radio frequencies in use. Most mobile service providers operate a network which uses multiple standards and a handful of frequencies while most phones are capable of operating with a handful of standards and frequencies.

For voice and SMS text messaging, there are two standards in use:

• GSM underpins 80% of mobile phone networks worldwide. GSM phones have a removable SIM card (subscriber identity module)