Using a 3600HGV gateway on a new line

Hi,

I have two friends that are att dsl users. One, G, has the 3600hgv dsl gateway and the other, L,  has the motorola 2210 dsl modem.

G, with the gateway is moving to the house of the friend, L, with the modem. They would like to use the gateway because it has a wireless router. So the question is, other than the physical connection changes, what do I need to do to swap out the modem for the gateway? How do I get , G's, gateway to recognize and log into the att servers on, L's dsl service?

When I log into the 3600 I do not see a place to update the att user name and password.

Thank You

MC