Make and receive calls on the Internet
No carrier minutes, no roaming, works without a SIM card
No connection fees, maintenance fees or any other hidden fees
Your contacts don't need to use the app, they can call you from any phone
O2 VoIP is the simplest and best app to make cheap internet calls.
O2 VoIP is based on CSipSimple and is licensed under GNU GPL v3. More information in the app.
Try it for free.