20-25 minutes for 8GB with max 3Mbps down is straight up lying. it's not even a matter of the technology behind it, it is mathematically incorrect.
when i had AT&T i got around 7Mbps down and like 0.1Mbps up; it was ADSL so they throttled download. you can't say "the advantage of fibre-optic is speed!!" when you're offering one of the lowest apparently acceptable speeds possible. this is the kind of thing that's just blatantly anti-consumer and abusive.
to be fair, their actual website has more accurate numbers for the sizes provided:
http://www.att.com/shop/internet/u-verse-internet.htmlof course they're very vague and the average consumer doesn't really know what it means except what they tell them but w/e