First you need to call T-Mobile and ask them to enable international roaming on that phone number, there is no charge for this but they don’t automatically do it you need to ask for it.
When you are in Costa Rica and call a number in the states you dial 001<area code><number> the caller id will show up as your normal number nothing different. If someone in the states calls your number while you are in Costa Rica your phone rings just like normal.
The charges for voice calls are $2.29 per minute both incoming and outgoing. If you use data you will be charged $15.00 per MB.
There are many cheaper alternatives.
Tmobile service does not work at all in SJO. If you have a phone that supports either UMA (blackberry) or a newer android phone that supports wifi calling you can place and receive calls using your number in most places that have wifi.
If your phone is not carrier locked you can get a SIM card from ICE before you leave the baggage area at the airport. This will replace the phone number with a local one. All calls will use this number. If your phone is still under contract tmobile won't give you an unlock code.
I know that wifi calling worked in the SL and Dunn Inn.
Go on ebay and buy an unlocked cell phone for $50, 3g if possible for a little more, and buy a SIM card at the ICE kiosks at the SJ airport or elsewhere and make your calls. Your caller ID will show up as "unknown" or with the actual sim card assigned telephone # depending on if your calling a regular USA tel or cell# or if calling a Magic Jack number. Search SIM cards on this board and you'll find a wealth of info.
