Hello, it doesn't really matter if you bring an unlocked phone or not. Ive always spent like around $90EC ( ~ 36 US) on a phone from LIME which comes with $10EC on it already. The cell phones on the island are majorly prepaid. Incoming calls are free. Digicel to LIME calls or vice versa are always expensive. Ive always stuck with LIME and have never had any issues. Where as many of my friends with digicel admitted to having many issues (but thats just people that I know...everyone will have their own opinion). I did eventually bring down an unlocked razor phone at one point, and then within the past year an unlocked iPhone. I didn't use the iPhone much, I guess I was just paranoid that someone would see it n just snatch it out of my hands :P But thats just my paranoia. A lot of people have iPhones, Blackberry etc.
The cheapest priced phones you get are obviously not all high tech. So if you are okay with just having a phone to make calls, and not all those cool features then I think you'd be totally fine with a phone from LIME or digicel.
During the 1st week or 2 of orientation and classes, there are usually tents set up on campus from various companies i.e LIME, digicel. So you can totally get a bit of a discount if you purchase a phone/SIM card then. I believe if you ONLY buy a SIM card its about $30 EC??
Also in the beginning of the term they have something called "double bubble". If you add $50 EC worth on your cell, it doubles. But there are some restrictions to it i.e only LIME to LIME, use it with in a certain amount of days yada yada. I believe digicel does that as well.
I'd def go with LIME. But again thats my opinion.