Installation costs for some customers won't be required but for me it was free due to the following reasons.
Cost of installation originally was $149 but reduced to $75 because of offer. Once the installation was made speeds where at max 7mbps down with 1mbps and not the speeds I wanted. After AT&T sent out a line tech to fix a possible splice in the line at the pole the problem still persists. I downgraded to 3.0mbps/768kbps due to poor line issues. Then was given a 12 month promotional offer due to problems at installation reducing $10 per month for the cost of service.
Modem is $100 upfront but with mail in rebate that covers the entire cost of the modem and takes about two billing cycles to receive.
First month bill you will be paying a prorated charge for the service and the second month including any installation fees and modem cost. I haven't received my bill yet but I will update the review when I do.
So far service has been stable and consistent and I have been using it with my new google tv from Sony without any issues besides HD video but I just need a faster connection than 3.0mbps for that.
EDIT 2012-04-01: Although the connection is stable the modem provided (Motorola NVG510) is not and sometimes it would lock up. I only write this after this has happened to me a few times for the last few weeks. Restarting the gateway fixes the issue but it gets quite annoying when you heavily use the bandwidth and randomly your connection dies.
EDIT: 2012-06-21: After a few months of owning AT&T service I will be moving towards Comcast business class for a double the price because I need the speeds. After several attempts to have AT&T do something in my area for speed upgrades and got nothing I will be taking my money elsewhere. If you need basic internet access for most regular tasks then AT&T is a viable option for you, but if you have a home network with several computers then this won't be for you.