Asterisk VoIP over mobiles
This software installs on your phone and gives you cheap calling from your cellphone and is really an extension of the international callback services that were popular a few years ago. Run the java app, enter the number to call on your phone and you get an incoming call on your phone. Answer that and your call is then connected to the other party. I only had 2 min trial and the product isn't really suitable for the NZ market due to the high termination costs (since you are baing charged for the call to your mobile and then the destination).
It's hard to really see a market for products like this anywhere but the USA where you're not paying big $$ for mobile termination. I've got a similair setup at home right now running through my Asterisk PBX where I can send an SMS to my SMS gateway at home or access a similair page via WAP which will either ring me back on my mobile (or any other number I select) using italk VoIP and then connect me to a destination number in NZ.

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