When I install the Cisco IP Communicator (soft phone) version 22.214.171.124 on my computer, I can see it gets a dynamic assigned number (6651478) from our "Cisco Unified CM Administration - System version 126.96.36.19900-2" installation.
If I make a search in "Directory Number" in the "6651", I get 526 search results back (from 665100 to 6651522).
Does this mean that if I install the "Cisco IP Communicator" soft phone on 527 computers, then the 527'th computer do not receive a phone number? Or is there another boundary in the dynamic number assignment?
As well as Mark indicates, the server appears to be configured with auto-registration.
Look this from the CUCM System Guide:
"When you enable autoregistration, you specify a range of directory numbers that Cisco Unified Communications Manager can assign to new phones as they connect to your network. As new phones connect to the network, Cisco Unified Communications Manager assigns the next available directory number in the specified range. After a directory number is assigned to an autoregistered phone, you can move the phone to a new location, and its directory number remains the same. If all the autoregistration directory numbers are consumed, no additional phones can autoregister with Cisco Unified Communications Manager."
If you like to read more:
Hope to help.