Cell phone with SIM card for use in South America?

I have 2 friends, one from Argentina and one from Peru. They are both visiting the US, but when they go home, they want to have a cell phone they can use in their countries. One of the requirements is that the phones must have a SIM card. I was wondering if anyone knows of phones like that or a good, reliable website they can buy them from. Also, one if them wants a touch screen phone with a slide out qwerty keyboard. Anyone know of such a phone that can be unlocked? Their budget is around $100 or less (preferably less of course). Can anyone help me find good phones for them? Thanks! :)