turning off dynamic ext helped a little bit:
Scenario 1:
if I'm on a local phone call with someone else here in the office ie x4325 and someone else from x4399 calls me it will ring busy (great!).
However if I'm on a local phone call with someone else here in the office ie x4325 and someone external calls me from ie. 212-555-1212 it will just keep ringing.

Scenario 2:
if I'm on a external phone call and someone calls me locally is will have a busy signal (great!)
Scenario 3:
If I'm on an external call and someone else calls me externally it will keep ringing.

solved half my issue, thank you, any other suggestions?