The use of roaming SIM cards in its most common form is in normal voice applications such as mobile phone calls.
The common application of roaming SIMs for voice is where mobile calls are automatically routed to, and made on, the least cost network.
Some providers achieve this automatic call interception and callback by encoding a program onto the SIM card.
[2] For some applications (particularly where regular travel between two countries is the main purpose) a Dual SIM can be considered as an alternative.
Voice over IP apps (softphones) may be installed on smartphones to inexpensively call international numbers.