If you are refering to the technology where you need to enter a username and password to log in, like most ADSL providers in the U.S., it is posible. The Gateway will need to register to a gateway. I will re-register on the gatekeeper every few minutes, that way when the provider change you I.P. address, the gatekeeper will “refresh” the information, and keep the routing of the calls to you.
Most likely it could be done with a lot of diferent gateways, but the only one that i have experience with is a Quintum Tenor A200 with a Tenor A800 gatekeeper/gateway.
They use to have troubles with the registration process, but the lates version of software of the A800 (version 19) ,fixed the trouble.