at&t M8 Lollipop OTA Update today?

From what I remember when I worked at Sprint, each carrier has it's own iOS version in the sense that the radios are locked to that carrier, so like you can't just walk over to Verizon with your AT&T phone and you're off to the races. It has to be unlocked and all that. Other then that iOS is not different on an AT&T phone then it is on a Sprint phone. I think you they may have some things like the basic MyAT&T app on there, but that is treated like any other application and it just loaded on their by Apple. Not 100% sure about that one, I've never tinkered with a carrier locked/branded iPhone.

I don't think the carriers can tinker with iOS like they do Android, they can just test it.

Actually for the US carriers Apple handles all the testing as well. They bought the necessary equipment to do the carrier testing in-house. They want the carriers to have as little to do with their hardware/software as possible. They don't even allow MyATT preinstalled. LOL. They make the carriers submit their apps to the app store like every other developer. Say what you will about Apple's closed system, but it works for them, and a majority of their customers as well.
 
Been using it for three days now.
The only downside, it now takes three times as long to boot up in the morning, I do a complete shutdown at night.