When I was in Mexico I used Skype to call my family at home (landline). Some years back I bought 10Euro worth of SkypeOut credit, and I've still got lots left.

The calls worked fine from Mexico, but wi-fi connections may be hard to find. There was free wi-fi at my (relatively expensive) hotel, but no such luck at many other (some also expensive) hotels. There's free wi-fi at some airports too, at least after going through check-in. Outside the check-in area the access points appeared to be of the CC-pay type.

Mexico supports GSM phones, but the coverage is spotty outside of towns.

EDIT: Oh, and if you're getting a car, don't drive at night - you'll find the mother of all speed bumps on some of the roads, you literally have to stop the car to go over. You don't want to run into any of those in the dark. And use bottled water for _everything_, don't let any local water touch your lips or toothbrush. Bring some medical whiskey or something, use it to clean your toothbrush in case you accidentally forget yourself (like I did, with dire consequences). The water is probably fine if you're used to the bacterial flora (i.e. if you live there), otherwise don't take any chances.

I just came back from Mexico & was very disappointed that the ritzy resort we were staying at (Gran Bahai Principie, an hour south of Cancun) didn't have free wifi. And the times we left the resort we were going touring, so no time to drop into a coffee shop or such. So I used my N810 mainly just for GPS & watching video on the plane. My 4 year old son used his N800 to draw & watch videos.

And I second the warning about those speed bumps. Nasty. Especially the ones with the Policia hanging around with their nice automatic weapons

Skype can make free calls to US toll free numbers as well as from other countries like UK, France, etc.

Thank you guys.i am also going mexico..thanks

Skype still works, but Gizmo5 is gone. They were bought up by Google and their servers were finally pulled earlier this year, around April 2011.