You need to have GSM (International) support for the phones, a SIM card, and a plan that enables this support. It will cost $1.50 per minute. I use SKYPE form my room over the internet. Your best bet might be to rent a few phones here.
http://www.arubafastphones.com/
http://www.setar.aw/index.php?option...per&Itemid=140
Here is a thread on SKYPE:
Skype Wi-Fi Phone