iphone version from at&t

Since it came out forever ago, at this point it will be 2.2.1.

 

If you want to use it with another carrier down the road, simply jailbreak it. People have succeeded with a jailbroken iPhone on T-Mobile, Vodafone, and other carriers.

As for AT&T, you can expect the specific iPhone unlimited data plan, as well as the option of Visual Voicemail.

If you bought the iPhone 3G now, it will come with 2.2.1. If you buy it when the new OS and phones come out, it may or may not have 3.0 instead of 2.2.1, but you can downgrade to 2.2.1 from 3.0 if necessary.

 

2.2.1+ has a non-unlockable baseband thus far. Can't unlock it, only use a turbo sim.

You can jailbreak however.