I got the same error you got. "Network Busy". It turns out that Google is adding a + sign in front of the outgoing numbers. Mine was fixed yesterday, but now it's messed up again.
Here's the thread that I've been posting on over at Google Help:
Network Busy Error with HTC Eris - No Outgoing Calls - Google Mobile Help
For now, I'm using the app GV Dialer. I wrote detailed instructions at the end of that thread too. Good luck!