* i've checked the modem model you posted and yes, it should work. technically, any dsl modem will work with att internet. however, att encourages you to use att-provided modem because of scope of support benefits.
* once you get the modem, it has to be set up or configured so it can get connected to att. you will have to go to the modem's page and enter a username and password that will authenticate you to the att network. with an att-provided modem, att tech support can assist you in all those steps. if you get actiontech, att can provide you only with the username and password, but not with the setup. for the setup, you may contact actiontech support (1.888.436.0657), or download steps online if possible. the actiontech package may also provide a quick guide to set up the modem worry-free. make sure that you have the username and password before you contact actiontech. also make sure that the username and password att will provide you are the AT&T member ID and the DSL Network Password.
* if you haven't bought actiontech yet, you may look for other att-supported modems, like Westell 6100. it works a lot better than motorolla. if you use wireless, you may also want to check out Westell Versalink 327W or 2wire 2701 HG-B Gateway, which serve as a modem and a router in one. But of course, those last two will cost more haha. the motorolla you will receive, is it within warranty or have you been charged for it? because if you are paying, if ever you get any of the modems i mentioned in a nearby store, you can actually just return the Motorolla modem as soon as you get it. you have to call tech support to process a return label for you.
* well anyways, sorry for the long post, but if you are capable, you may purchase the actiontech modem so that when you get the motorolla, you at least have a spare modem with you (whether it would be the motorolla or the actiontech is up to you).