Mexico - Smartphone rental(?) for a month

I'm going to Merida, Mexico for almost a month. My current US smartphone is not capable of going on global networks.

What are my options for getting a phone to use in Mexico for a month? I'll be transiting through Cancun, so something either in the airport or around the ADO bus station would be ideal. Alternately, I'll be spending 3 of those weeks in Merida, so that could work as well.

I'd like something for light mobile internet usage (to use maps, the occasional internet page lookup, and instant messaging), and that could text back to US numbers.

http://www.mexconnect.com/articles/3190-short-term-cell-phone-in-mexico-for-only-14-us

I remember when going to Seoul, Korea, they would rent cell phones for a $1 per day, but I don't remember if they do the same thing in Mexico. I used to have an AT&T phone with international service, but it was very expensive to call within Mexico. I would buy a short-term disposible phone in Mexico. The article above has some tips, but perhaps others have more ideas.