OneSim VoIP is a mobile application designed for OneSimCard customers, enabling them to make and receive international calls at reduced costs. Users can utilize the VoIP feature over a stable Wi-Fi, 3G, 4G, or LTE connection, choosing between the OneSimCard SIM or VoIP network when making calls. This flexibility allows for significant savings compared to standard international roaming rates. Incoming calls can also be routed through VoIP if the device is registered online, otherwise, they will be received via the traditional SIM card method.

The latest version of OneSim VoIP introduces a texting feature, enabling users to send and receive SMS to and from US and Canadian numbers at lower rates than conventional roaming SMS services. While a OneSimCard SIM is not necessary for app functionality, users must have an active OneSimCard account and a VoIP-enabled Personal Extra Number (PEN). Initial setup is managed through the OneSimCard online account, ensuring users can easily create and manage their VoIP settings.