It's not easy. and the outcome won't be 'great' more like mediocre. but you'd have to use VOIP. a good program for wm is PortGo.
so a free sip voip provider like Whistle
have your googlevoice calls forwarded to your Whistle phone number
have your whistle sip account set up in PortGo.
now you can use your tp2 as a wifi phone.
like i said, a time consuming set up, but will work.
here's the portgo thread on xda-developers:
[APP][UPDATE Aug 23,2010] PortGo(PortSIP CE) VoIP/SIP free softphone - xda-developers
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