I bought prepaid virtual phonecards at the www.belizeans.com
website for calling Belize. The rate is $.0188 per minute which is the cheapest I have found anywhere. It has great rates to Panama too (and presumably anywhere else, you can do a search for any country) and also good rates for calling within the US.
You order online with a credit card in increments of $10 or $20, and they email you a PIN Number and the access number to dial.
Go to www.belizeans.com
and then click the message board and click the link that says "buy phonecard" (link may be on the home page also...)
They also sell prepaid cards that will work for calling the US from Belize. They only had one card on the menu for that and I think it was around $.56 per minute or something like that which less than ATT, MCI, etc. will charge you for using their cards...and don't even think about what it costs to dial direct to the US from a phone in Belize...ouch!