Playing Heroes 3 over a 3G modem.

I can't connect with my friends using a 3G modem. Before, we could connect normally when I had a good internet connection. In my new place, there are no internet providers yet, so I'm using a 3G modem. We connect through Hamachi. The connection is established, and the game shows that my friends are connected. But as soon as I start the game, problems begin: data is being transferred (or received, if I'm not the server), the percentages fluctuate, sometimes it's 13%, then 96%, then 19%, and it freezes at some value, and then nothing happens. I exit using Alt+F4, and my friends can play without me... Please help me figure out the problem.