Call Waiting issue

Ubuntu 10.04 64bit
Asterisk 1.8.3
FreePBX 2.9beta

I have Callcentric for a for my main provider. I have setup google voice sucessfully for free US outbound calls. When I am making a outboud call using gvoice and try to call my home phone from say my cell, I get the message from FreePBX that “Extension # … is busy”. So how do I get call forwarding to work with callcentric while making an outbound call with gvoice?