Getting googlevoice, gizmo, and sipdroid to work over 3g on a droid 2?

So I have a droid 2 through verizon with a data and text only plan. I have set up google voice, in conjunction with gizmo5 and sipdroid in order to have free unlimited voice. It works great within the range of a wifi connection, but will not work at all when relaying purely 3g. Is there a setting im missing or something I need to change? I followed these instructions to set it up: http://davestechshop.net/VoIP-on-Motorola-Droid-With-Sipdroid-Gizmo-GoogleVoice-Free-Calls. Constructive answers only please from those who have experience doing this. Thanks!