RoamTheWorldCellPhones.com

Cellphone GSM Frequencies: 1900

(This means you will need a GSM cellphone that will work on 1900Mhz to use it in Mexico.)

Cellular carriers for Mexico

Pegaso PCS, S.A. de C.V. (movistar)

Frequency: GSM 1900
Website: www.movistar.com.mx

Coverage Map

Radiomovil Dipsa SA de CV (TELCEL) (TELCEL GSM)

Frequency: GSM 1900
Website: www.telcel.com

Coverage Map

If you've used either of these networks or roamed in Mexico, please post about your experience and the cost. Feel free to ask questions.