Shinkyo, The 3G Ipad Can Be Used As A GPS
But has some limits like patspad stated above. I'm hoping someone from Mexico can advise you on specifics on how to get a sim card for your iPad. I believe that Apple has set up agreements with each country's major carrier(s) for cellphone service to serve the iPad. In some countries like Canada, I think you have more than one carrier. Mexico might be similar. In the USA, we only have one choice so far.
With a 3G iPad you can get at the very least an idea of where you are. I also use MotionXGPS. This is a paid app but worth it.