What's the best way to use Google Voice with my AT&T iPhone?

I have an iPhone, and my minutes usage is well within bounds, but I have the $15/mo 1,500 SMS plan.

I love Google Voice SMS features (like shooting out SMSes from my laptop). The problem is ppl often ask me who I am, since they don’t have my Google Voice # on their end.

I want to avoid having to give all my contacts a new #, so I rather take advantage of AT&T’s call-forwarding.

Does anyone have suggestions on how I could take advantage of Google Voice + iPhone?