This issue occurs if you are using an H.323 gateway to connect to the Public Switched Telephone Network (PSTN), and no calling party information is being received.
In this case, the gateway uses the destination pattern of the first plain old telephone service (POTS) dial-peer associated with the voice port. If you have a POTS dial-peer with a destination pattern of 9T, the incoming call picks up the 9 and presents that as the calling party number.
If enabling caller ID is not an option, you can prevent this behavior by using the following procedure.
Remove all the POTS dial-peers that point to the voice port.
Make a new POTS dial-peer with:
destination-pattern . (notice the period after the destination-pattern)
port number (for example, port 1/1/1)
Paste all the other ones you had back in. The phone then displays "From Unknown Number" rather than "From 9".