GrandDialer is a free application available at the iTunes App Store. It's basically like using Click2Call from your iPhone.
It's not a VoIP solution. You still are making the call from your iPhone, so it's not a solution that would turn an iPod Touch into a cell phone.
However, you could use an iPod Touch to initiate a connection between some other cell phone and the number you wanted to call. Your phone would ring along with the other person's phone, just like when you use Click2Call, and both calls would show your GrandCentral number on the Caller ID.
GrandDialer is available from the iTunes App Store.
