Prepaid might not work for int'l calls.
I use a prepaid cell as my regular cell phone (I don't use phones often; this is only for travel and emergencies), mine is from Virgin Mobile, which has the best per-minute price by far, no roaming charges, and really cheap IM for a prepaid. (Last I heard, Tracfone didn't offer IM, but that could be out-of-date info.)
Just so you know, in the US, prepaid cell phones are not really good for int'l calling. The per-minute and access charges are VERY steep, when access is available at all.
If you are going to be phoning home, just buy a regular landline calling card at someplace like Wal-Mart. Those are less than 3 cents per minute for domestic calls, about 15 cents per minute for int'l (to S. America, anyway.) The access is an 800 number, so you can use any payphone or your hotel phone to access that for little or nothing.
BTW, if you are going to buy a prepaid mobile, I'd order it online a few days before you leave home, and have it delivered care
of your hotel. They should not have an issue with holding the package for you for a couple of days if you call and let them know.