When it says (GRP) that means that those phones which display that means they are in a Linear or UCD Ring Group. When a call comes into that kind of ring group, it will ring first one for so many rings, and then next phone until all members are rung then it goes to call coverage.
To View them, log into GUI of unit, then go to Voice > Ring Groups.
Mark, when i try and answer the (GRP) call, the second i pick up it's gone and rings to another station, try to pickup that station its gone rings to the next one so-on and so-forth
Ok, yeah it is not supposed to act like that.
Can you run some debug for us via the CLI and post it.
Debug sip stack messages
Debug voice verbose
Debug sip cldu
Also what version AOS you running on 7100 and what firmware you have on your phones.
Are all the phone 706 or do you have different models?