AT&T, T-Mobile, and Sprint seem to be fine in the island, different member of the forum use them and they seem to be pleased. Some have complained about Sprint but not everyone. There are other local MVNO but I recommend you stick with the main ones for now. If you are already using any of the above ones, there is no need to re-start your contract, you can keep the stateside contract. If you want a local number you need to ask them for a local number but you don't have to either.