Unless you have an old phone, most newer AT&T phones have world phone capability, meaning they are either tri-band or preferably quad band GSM phones. Quad band will work in a wider range of countries. For CR, the important thing is that it works on the 1800mhz band.
I'm not sure what plan Travelman is on. MY understanding of AT&T policy is that their "World Traveler" plan is $5.99 per month (PLUS taxes) and NOT just $5.00. Also, their "discounted" World Traveler per minute rates for CR is $1.99 per minute (PLUS taxes) and NOT just $1.29. On the plus side you don't have to sign up for the full month. You can call and ask them to activate it for just while you're down in CR and only get charged the pro-rata portion of the $5.99 for while you actually have the plan active (plus any per minute usage of course). OTOH, their regular international roaming rate is only $.30 more (or $2.29/minute). So you only save if you call at least 20 minutes or more (admittedly not that difficult) or spend at least $40 (PLUS the pro-rata monthly rate AND taxes)
http://www.wireless.att.com/travelguide/coverage/coverage_details.jsp?CIDL=188&MNC=CING
If you only make rare trips to CR (which many of us don't) and if you plan to rarely use your phone (keeping it only for emergencies (such as making it possible for the folks at home to reach you at any time) then the "World Traveler" plan MIGHT be your best option. HOWEVER, there is another option which might be even better.
It involves "unlocking" your phone and getting a different SIM chip. AT&T tries to make this very difficult if not impossible because, obviously, they'd rather you use their expensive service. However, its your phone and you should be able to use what ever carrier you want with it. Here's what you have to do. If you've been a AT&T customer for a long time (at least a couple of years or more), you can call to ask them for the unlocking code. IF they won't give it to you you can also find out what the unlocking code is for your particular model of phone by going on-line. Typically, this will cost you ~$8.
Once it is unlocked you can open up the back of the phone and switch SIM chips, which brings me to step 2. You need to get a SIM chip that will work in CR and ICE is not particularly good about sharing their access to phone service in CR. However there are chips that will work in CR. One that has been recommended to me is Celtrek (
http://www.celtrek.com). Their chips start at $74 and those include 25 minutes of airtime. After that their per minute rates are just $.37/minute in CR, $.29/minute to the US and $.19/minute for incoming calls. Still not super cheap but a hell of a lot better than anything else we've been talking about up to now. Granted, if this was a one time trip, with all the overhead of unlocking the phone and the $50 base charge for the chip, this still not be for you, but I calculate (assuming 50% calling in CR and 50% to the US) you'd break even after about just 45 minutes of calls (~$90). After that your AT&T charge would continue to compound dramatically, but the SIM chip would only grow at the $.29-$.37 rate (did I mention you can also reload the SIM chip with more minutes at any time).
There are some other negatives. For example, with a new SIM you will have a different cell phone number. This might actually be a good thing if you plan to give out your number to any chicas. It might also be a good thing if you plan to limit who can call you from the US as you can just share your traveling number with those who you want to be able to reach you. It is also possible to set up your regular number to forward to your new number (perhaps others can detail what is involved with that). The other drawback is that there may be a more complicated connecting procedure such as connection codes that you have to prepend to the number your are calling. With CelTrek you place the call just as you normally would but then it gets queued for connection and you hang up the phone and a second or 2 later you get a callback when your connection is ready.
Does all of this sound too confusing for you? There are also cell phones you can rent in CR or you can just wait until you get to a public phone (which are still fairly common in CR) and use a prepaid card. Both of these will probably get you lower rates than your AT&T service depending on how much you plan to use the phone.