I did that as a backup plan, but didn't use it because the per minute charge for me was $1.50 per min - even for local calls. With the ISM chip, my incoming calls were free and the outgoing (for local) cost something like a quarter or 35 cents. No rental and no worries (or potential conflicts) to show up on my phone bill later on. And the chip comes with a Mexico phone number you can give those who you want to reach you (and not give to those you don't!) THAT is critical. The phone must either be a Telcel phone originally or be an 'unlocked' phone which works in the 1900Mhx band. Phones you find in the US are all 1900 Mhx I believe, but phones in Europe work at 1800Mhx, which won't work in Mexico (or in the US).