What I did was:
- Went to AT&T store, got them to port my home number into a prepaid cell. IIRC this cost $25.
- Then I signed up for Google Voice, and requested a port of the number. GV would only port a cell # which is why I had step 1.
Once the # is in google voice, you can have it point at the Obi, or you can have it ring on your cell phone. So it's a way to keep your land line # without having to keep your land line.
Google seems to promise free Voice service only one year at a time. So there is some risk they might start charging or discontinue the service at some point in the future.