I take it you've never used the Google Voice application for Android/iPhone? On my android phone the text message issues you've mention disappear as there are no forwarding numbers and every message arrives on my phone.
I have used the Android app a little bit, the integration looks great on the surface. The problem (as I understand it) is that the GV app uses data, which means it uses more battery than just SMS, and doesn't work as well in low signal circumstances. I don't have first-hand experience of this though, and I can imagine for some people it wouldn't be a problem.
The Android app is terrible in low signal situations. When sending a message it blocks the entire app with a "Sending" modal window. I don't know how they could've fucked that up so bad. If you've going in and out of service you have to kill the app and reopen it to even get back to the inbox. I can't imagine why they didn't just show the message in a pending status the way the standard SMS app does.
