Global System for Mobile communications

or


Time Division Multiple Access

I think anyways.......

I don't know what those expanded initials mean.

GSM is what most of the rest of the planet - outside of the US uses. If you plan to travel abroad you need GSM.

TDMA is what verizon uses but outside of the us it's not widely used.

It's a sort of beta vs vhs kind of thing. Many technologies came out at once.