I'll share my Porting story. It originally went from a Landline, to Vonage, then to Ooma for 20 years. I switched to the free plan for Ooma (only playing taxes which came out to like $5+ a month). I then decided to take the journey to port it from Ooma to Google Voice. I decided to use Ting vs AT&T (my primary carrier) cause it seemed like the cheapest way to do it. I bought a $6 sim card at Best Buy to get ready. The thing never worked, so Ting was nice enough (their customer service was great all along) to overnight a new Sim to me. After about 16 days it finally ported over. I then needed a new phone to do the verification on. I went to Amazon for a cheap $16 GSM unlocked phone and found one. The instructions were worthless, so went back on Amazon and figured out eventually to get it going. Never signed up for any minutes/plan with Ting, just got the verification call and it was good to go. After that, it took 24 hours to port over to Google Voice.
I bought the OBi200 (a used one on ebay, wish I saw that sale) to use with it. So far so good with the call quality. Only thing I don't like about it is the no name under the caller ID. But I don't get many calls on it, so it's not a big deal. The one thing I am looking for is 911 service, haven't figured out how to sign up for that yet (if anyone wants to show me I'd appreciate it!). Don't want to high jack your thread, but besides that I'm pretty happy with Google Voice and the OBi200.