I was on Pageplus with my flip phone until mid-February 2014. My plan was $10 for 100 minutes. I had to do another deal within 120 days or all my minutes would expire. Unused minutes would roll over. When I got my Nokia Lumia 520 (locked to AT&T), I decided to keep my old flip phone for a while and see if I got 1/2 decent coverage with the AT&T Lumia 520, so I have a new number. Keeping your old number should be easy.
I'm on Airvoice now with the Lumia phone, cancelled the Pageplus account, forfeiting my minutes. The Airvoice plan I'm on is $10/month, I have automatic refill set up through Prepaidonline, the same way I did with my Pageplus account, it is a bit cheaper that way and I don't have to attend to renews.
My Airvoice plan includes data and voice/text, and unused usage rolls over. There's a cheaper plan I'm thinking I'll investigate with Airvoice which you renew every 3 months instead of monthly, also $10/month, and I'm going to maybe convert to that because I already have ~$60 worth of unused minutes. Hopefully, I can use those accumulated ~$60 worth of minutes with the $10/3month plan if I switch. I just use very little data (use wifi at home a lot), and rarely make calls with the cell phone.
AT&T works OK for me when not at home, but in the house my coverage is spotty at best and I don't make calls on the Lumia at home, I just use my land line. Verizon's better around here, a lot better, but the Lumia's don't support Verizon the last time I checked. Anyway, my phone was $30 Thursday morning, which strikes me as an incredible deal. It's my first smartphone and I have little reason to complain, a lot to cheer about.