I use Voip.ms for this purpose. I had a number through AT&T, which I then ported over to these guys for $25. I then set up call forwarding to my primary phone,

I use Voip.ms for this purpose. I had a number through AT&T, which I then ported over to these guys for $25. I then set up call forwarding to my primary phone, which costs $0.0205 per minute.