MobileVOIP offers cheap national and international phone calls via a Skype style application. The difference is MobileVOIP works with multiple network providers all offering different calling rates.

The app itself looks quite slick but the problem is you have to go to each network provider's site to view their calling rates - there's no convenient comparison table.

Some users also report that both call quality and stability isn't great so our advice is, stick to Skype if you can.