There are two GSM providers in Mexico, Telcel and Movistar. Movistar is cheaper, but its coverage is vastly inferior to Telcel. There are major Mexican cities where they have no coverage.

Who is your current provider on this phone. TMobile USA has a Blackberry International plan which will cover your US e-mail in Mexico for $19. ATT sells Mexican roaming buckets. You might be better throwing a Mexican prepaid SIM in a cheap unlocked phone and doing your data with one of these plans. You need to do your own math here. You also need to assess your own Spanish skills.