I have premium account with 4 phones, 4 users. I added presence to all phones. The phones I am using are Polycom VVX250. There are 4 lines on the phone. When I changed the line options to 1, the user is labeled on line 1 of the phone, lines 2 and 3 show 2 other users, but line 4 is blank. How do I get the 4th user to show up on the phone on line 4?