Joining ring group

Is it possible for a user to dynamically join a ring group ?
I have a user who is a sales person and a tech person and I would like him to be a member of both groups, but he should be able to “log out” of one group if he’s busy helping the other group.
Is that possible with asterisk 1.2.15 ?

If not how is something like that handled with asterisk ?

Thanks
JB

The agent interface allows a user to sign in and sign out. Not sure if it allows one physical end point to sign in as more than one agent, though.