Hello All,
I've had a G1 for close to 5 months now. I purchased it with the sole intent of using it OFF of the cellular network, and only for the purpose of having the Google Voice app, as well as Sipdroid, as a much smarter 'home' wifi/voip phone..
In this time I have not had the same experience as the OP, I did have SMS forwarding turned on for a short time(with a prepaid SIM), but after that, it still took up to 5 minutes to receive new SMS messages. I now have the Droid configured to have SMS from VZW forwarded to the phone, and the set not to display notification of new SMS, so basically, my Messaging app will always be full of new unread SMS. Looking at my Account shows a ton of incoming messages and no outgoing messages.
As for calling in/out. Download GV by Evan Charlton from the Android Market. Configure it to route all outgoing calls through his app, and disable the official Google Voice app by setting it to 'Do not route any calls through Google Voice'.
This will cause all of your outgoing calls to actually be incoming calls from your GV number, which for some of us, means free outgoing calls... albeit in a round-about fashion.
Until the official Google Voice application is updated to call your number instead of some random changing number, this is the easiest solution. Though I'd imagine this implementation gives the Carriers some peace of mind..
The GV app can also be configured to route calls back via a Gizmo5 747 number, which unless you already have it, you're not going to be getting one anytime soon, as Google just bought Gizmo5 and shutdown registration..
Though in the long run, that should mean very good things for us. possibly: the ability to make/take calls from any computer with a microphone and speaker. Or simply pure SIP calls from inside the Google Voice app over the Droid's data connection. Or if we're really lucky, they'll just buyout what's left of Sprint, and start selling internet-only android devices on which Google Voice runs perfectly.. Maybe I'm dreaming.