1SIM VoIP is a mobile application designed for OneSimCard customers, offering a cost-effective solution for international calls and texting on iPhones and iPads. Users require a reliable Wi-Fi or mobile data connection along with a VoIP-enabled Personal Extra Number (PEN) from OneSimCard to utilize the app's features. With 1SIM VoIP, users can choose between making calls through the OneSimCard international SIM card or the VoIP network, providing cheaper rates for international calls. Additionally, the latest version introduces SMS functionality, enabling users to send and receive texts to and from US and Canada mobile numbers at reduced rates over Wi-Fi or mobile data.