Are you talking about calling or called number ? Calling number is definitely determined by Ext ph mask setting under each phone. This is the caller id that people will see in the pstn. Looks like your gateway is h323 based. So in your route patterns (say 9.[2-9]xx[2-9]xxxxxx, your digit strip settings are set to none so that when you dial say 92142222001, the 9 is prefixed and sent to the gateway. The gateway receives the call and matches a local dial-peer say
dial-peer voice 1 pots
destination-pattern 9[2-9]..[2-9]......
port 0/0/0
this dial-peer will definitely match the number you dialed (92142222001) and then to forward the 10 digits to the pstn (called number) you have to use command,
forward-digits 10. under the pots dial-peer.
HTH
Sankar
PS: please remember to rate posts!
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus