The dev of 3GU is terrible with updates and never answers emails and doesn't work with a lot of programs. My3G, on the other hand, is created by the people who brought you MyWi.
If you have MyWi, you don't even need My3G, just enable the WiFi tethering and your iPhone will think it's on WiFi anyway.
If you have MyWi, you don't even need My3G, just enable the WiFi tethering and your iPhone will think it's on WiFi anyway.