This is how I put one phone into two hunt groups:
Have 2 of each button: Login, Log Out, Auto-In and AUX buttons on the phone, you can use the same login ID for both hunt groups if you want. When there aren't enough buttons on the phone I put the Login and Logout buttons in the softkey menu.
Login Group 1 Login Group 2
Log Out Group 1 Logout Group 2
Auto-In Group 1 Auto-In Group 2
AUX Group 1 AUX Group 2