MobileVOIP is the first real VOIP app for Windows Phone 7, beating Skype to Marketplace.
The app works over 3G or WIFI and allows 100% free phone calls to some destinations using VOIP gateways, such as 2voip and Actionvoip. For those areas where calls are not hundred percent free very cheap calls can still be made.
The app unfortunately continues to have the issues common to VOIP apps on Windows Mobile â€“ the sound is only piped through the speaker, so headphones are still suggested.
The app features:
The app is free and can be found in Marketplace here.