PolynesianMedic: I'm not sure what you mean by "without a T-Mobile phone or account"? Do you mean porting into GV directly from a land line number (POTS or VoIP), or from some other (non T-Mobile) mobile phone number?
Currently, you can't port a land line number into GV; Google doesn't provide that option at all. You can get around this, as the OP did; port a land line over to a mobile carrier supported by GV (currently only Sprint, Verizon, AT&T and T-Mobile, I believe), then port that number to GV. Users' experiences porting into GV vary widely, with many problems reported, depending on carrier, area code/prefix, etc, with no clear failure pattern and very poor support from Google.
The key to success is probably using either a T-Mobile or AT&T GoPhone prepaid number, and ensuring that you have the exact, accurate account information for that number before you attempt to enter anything into Google's porting system. For example, for AT&T GoPhone, you need to contact their customer service, and obtain the actual account number (which is NOT the same as the phone number).
There is a lot more information and war stories over on the GV help forum.