I want to get a cell phone that I can use in other countries not just the US. Where do I find out about that?

Question

I want to get a cell phone that I can use in other countries not just the US. Where do I find out about that?
I recently traveled to China and I discovered that most of the phones there are different from US phones and cant be used here, but there are some that are made to be compatible. I want to travel the world and be able to use the same phone wherever I go. I would pay extra for the sim cards or whatever else would be required to make the phone work in other countries.

Answer

ATampT is the only carrier with international capabilities!!!!