Here's where I ran into a problem. The installer correctly detected that my ADSL+ modem, a BellSouth/AT&T Motorola 2210-10, is also a router. However, it then gave me two options, neither of which I wanted. One was to use the 633GR to replace the Motorola. The second was to add the 633GR "behind" the Motorola and use them both.
To make a long story short, I discovered that the Motorola modem can be used as a router. Since it only has one Ethernet port, however, that didn't make much sense to me. Happily, it can be switched over to a "Bridged Ethernet" mode, and then the Trendnet wizard will find it as a regular modem.
I also wrote about that, so if you need help with a Motorola 2210-10 (BellSouth version only, as the setup menus are different in other AT&T service areas), please see Trendnet TEW 633GR Router vs. AT&T/Bellsouth Motorola 2210 Modem.