roaming

In cellular technology (mobile telephone technology), the use of a wireless telephone outside a specified tariffed geographic area defined by the service provider (which area is usually called the "home" area); outside of the home area, additional charges usually apply. [After FCC]

The use of a wireless phone outside of the "home" service area defined by a service provider. Higher per-minute rates are usually charged for calls made or received while roaming. Long distance rates and a daily access fee may also apply.