I found out very strange issue.
When call was made from CCM A to CCM B via ICT, from certain users calls are not going through (rec. busy tone instead)
Then i tried to change the Display (Internal Caller ID) on the affected users (by adding 1 more space between first and last name) and it works.
It happened for about 4 users
Is this the a from CCM 6.1.4 ?