Can you explain this statement? I use Google Voice 100% of the time between AT&T and T-Mobile, and the only number anybody ever sees is my Google Voice number.
When you asy "Google Voice" are you talking GrooveIP? Because yeah, if I do that people see my GV number. But on Sprint, if you turn on GV integration, you can call using the native cellular dialer and the other side still sees the GV number.
That may be intentional. Here, I know my N3 sits on the lower speed network when idle, and then bumps up to the higher speed network when moving any non-trivial amount of data. Perhaps your carrier has configured things to work that way there, too.
That may be -- I'm totally new to GSM phones, so seeing it switch between them made me think it wasn't a good thing.