From Zahin Telecom:
ZahinTel TP is a mobile application for Android and other smartphones, offering VoIP Calls from data enabled mobile phones (2G/3G/4G or WiFi) to any landline or mobile devices around the world. Features: VoIP Calls via Wi-Fi, 2G / 3G / 4G. Works in all Countries and all Networks across firewalls. Smooth voice quality. Echo cancellation. Uses very less bandwidth. For End Users: You will be prompted for the following while starting the app: 1. Operator Code - Get Operator Code from your VoIP service provider. 2. User Name - User name is provided to end user by VoIP service Provider. 3. Password - Password is provided to end user by VoIP service Provider.