First of all... does your telco allows this???
Many telcos won't allow you to send anything outside from the DID range you own.
What you're asking IS what should be happening.
Run some debugs on the GW for a test call, if you see the caller ID from whoever is calling in the setup and your mobile shows your main number... call telco.
HTH
java
If this helps, please rate
www.cisco.com/go/pdihelpdesk
HTH
java
if this helps, please rate