otherwise, buy a digicell phone for $69bz and load up with credit - if you're canny about it you can get triple up, and use the 1010199 1 as amanda suggested. If you don't need the phone when you leave or the minutes, i'm sure someone will be willing to purchase for a small loss to you.
Alternatively rent a phone through Diane at
Quicksilver belize - it's only $5usd a day with $10bz credit and you can add credit through Diane when you need it.