I'd like to suggest taking into account different subscriber line prefixes, when processing phone numbers in regard to the phone book.

At the moments there is (to my knowledge) neither a solution to use the contact app to dial numbers (outgoing) nor to look up numbers (incoming) if different land lines with different subscriber line prefixes are being used.

The only work-around would be saving every contact multiple times with all prefixes (e.g. 0,6,9 etc.) bloating the database - or assigning fixed subsciber lines to users.

For outgoing calls, there could be a button in the Call-List / Contacts-App to select the trunk a user wants to take,

for incoming calls, the subscriber line prefix could be processed as wild card * and the trunk could then be added in the display.