I've just bought a new Blackberry Pearl through my US provider (AT&T) but will be abroad for the next year in South America. I've heard a lot about unlocking phones for use with other (foreign, in this case) providers and would like to explore this option a little bit more. I would just like those in the know to weigh in on this--should I try paying for a code through on of the many online services, buy one through Ebay, or try my luck asking AT&T to do it? Any advice is appreciated.

Right then, from what I can see your phone "should" work there, BUT, it is extremely limited in frequency choice, and that could mean many areas where you wont be able to get service, the fact your going to a major area suggests you should be fine and have no problems, but if you aim to venture out and about you could find service a problem.
Now there appear to be 2 networks to choose from there, they have a 3rd showing, but it's not up and running yet from what I can see, but here are the details of what they have, hopefully you will be able to find the better one for you.

Corporacion Digitel C.A. (DIGITEL GSM)
Operator Name: Corporacion Digitel C.A.
Network Name: DIGITEL GSM
Technology: GSM 900
Network Status: Live September 1999
Web Site: www.digitel.com.ve
Coverage Map
Roaming Partners
United States:-
AT&T Mobility; 3G 850/1900
AT&T Mobility; GSM 850
T-Mobile USA, Inc; GSM 1900
AT&T Mobility; GSM 1900

Telcel C.A. (Movistar)
Operator Name: Telcel C.A.
Network Name: Movistar
Technology: GSM 850
Network Status: Live December 2006
Web Site: www.movistar.com.ve
Coverage Map; There isn't one, but you may find more info on they're web site, but this usually suggests coverage is so poor they don't want to show how bad it is, so the other one looks the better choice ATM.
Roaming Partners
None that are listed, but it doesn't mean they may not of changed this since the info was last updated.

The other one is called Telecomunicaciones Movilnet C.A., but I do not know what it's status is, the date given (estimated) for the launch was May 2008, so the info is pretty dated now, so may not be as accurate as it should be, but it was said to be using the GSM 850 band