Have you registered your Cell Phone in Mexico?
All mexican cell phones must be registered by April 10th 2010.
The process is very easy for Mexicans, all it takes is to send a Message with the CURP number (this is a unique number assigned by the government) .
Foreigners living in Mexico can register their cell phone through the company they bought it, showing their passport.
Telcel has a website explaining the process:
Click in the very right menu “Preguntas Frecuentes” and scroll down to number 17:
17. How do I register a cell of a foreigner residing in Mexico?
Foreigners must show their passport to the cell phone office or store.
So, you (a foreigner) should be able to register your cell through the store or company whom you bought your cell with your passport.
Here is a screen shot of the page. It might be a good idea to print it out and take it to the cell phone´s office.