I have an extra cell phone whose number I want to keep. Right now it's forwarded to another phone, but I pay too much for it. I want to port its number elsewhere and forward it (or maybe collect voicemail for it that I can get out somehow) for the time being.

What's my cheapest option?

Tracfone would be very cheap but also risky. $15 for a phone and sign up for the $5/mo lifeline service.

Risky because tracfone's terms of service seem to promise your number will be lost for just about any reason, and I'll testify that if your service gets messed up, customer service just isn't up to solving much beyond sending you a new sim and most likely causing your phone to be switched to a new number.

Also check out VoIP providers. Not as cheap as a prepaid mobile phone, but maybe a little easier to deal with, being more of a regular bill.

callcentric.com, $5.95/mo ($5.95 setup, $25.00 one time lnp fee) will give me unlimited call forwarding. i'm going to pay them $6/mo instead of paying sprint effectively half of $80/mo and they'll forward to my grandcentral number, which rings my cell phone and my sip phone in my living room.