Upgrading to a smart phone,need advice on a plan

We are upgrading from our dumb flip phone to a smart phone. We want an international plan where we can call anywhere from any place. does Mexico have a plan for my needs?

Also has anyone used ATT USA that is located in Chapala across from the Guad Farmacia and do they speak some English?

I know a couple of people that have AT&T here and it seems that the coverage is a bit spotty in some areas - and it is AT&T Mexico, not AT&T USA. I would like to find out more about whose network of cell towers that AT&T is using here as I am also interested in a smart phone plan on AT&T that is seamless for travel to US & Canada.

We used AT &T on Madero in Chapala centro.
Manager speaks English. They were very accommodating.
There were a selection of plans that cover North America.

Ok. We are going to stop by there Monday, but again I am looking for something that we can call to or from international areas, Europe, Asia, Australia, etc.

Where exactly is AT&tT on Madero Chapala Centro? Can you tell me what side of the street going towards Soriana and a land mark like the bus station or something or how many blocks down from the red light.
I thought the AT&T was on the left going into Chapala in those strip mall empty stores. This isn't in Chapala Centro.

Can you call from Europe, Asia, Australia, etc. to and from on T-Mobile with no roaming charges. I'm looking for a world wide international plan.