I have used VOIP over a satellite internet connection with a soft phone on a PC, and it sort of works. I didn't have problems with dropped packets or audio breaking up as much as a HUGE delay due to the latency. I was getting 600-900 milliseconds latency, so when I would say "hello" the other end would hear it 2-3 seconds later. It worked but I wouldn't want to do it long.

If you get 100 to 150 milliseconds latency on your 3G connection it might be ok. You will want to check with your 3G provider to make sure VOIP traffic is allowed, because come discourage it.