We are using Translation Patterns to have speeddials to mobile phone numbers. These speeddial numbers are 19 + your internal phone number. My internal number is 556, so my 'mobile number' is 19556. This TP translates to my real mobile number by filling in the 10-digit 06 number (06 is the prefix in the Netherlands) in the Called Party Transform Mask, and de 0 as Prefix Digit for outgoing lines.

This works just fine, though we have a few users (we have a total of 350 users) complaining that sometimes they get a busy tone when they call a 19xxx number. When they dial once or twice more to the number, they can properly reach it. They are sure the phone itself was not busy. And even if it were busy, they would hear the phone's voicemail, not a busy tone. It's not always the same number, it's always another speeddial number that has this issue.

We are using Cisco Unified CallManager 4.3. We have 75 ISDN lines (2x ISDN30, 1x ISDN15), of which an average of 20-25 are used and peaks at about 50 lines in use.

Is anyone familiar with this problem?