Verify their other phones. If I'm not mistaken the Treo 750 is a world phone wich means it has CDMA and GSM radios so that you can use it world wide. Some black berries come like this as well.
EDIT: I just checked and yes they do offer a series of GSM phones. Maybe they're running on both networks here in
PR? I know for SURE they are on CDMA as well. Now this doesn't make any sense, they DID buy Verizon Wireless of Puerto Rico and they were CLEARLY CDMA.