said by Paralel:
If this is so important, why people don't look into this before switching is beyond me.
Well, it's pretty hard to look into. You won't find this information on an AT&T web page. The Sales department doesn't know. Tech Support won't know what you're talking about. People in public forums will give you conflicting and untrustworthy information. A lot of time, all you can do is sign up and reverse engineer the product.