This short & simple dial-plan removes the 3 digit country code from incoming calls and then pushes it to our FPBX IVR.
nano /etc/asterisk/extensions_custom.conf
After opening the above ^, modify and paste the below into the bottom of the file.
Modify your SIP trunk context to reflect the name below.
[trunk-in] exten=>_X.,1,Verbose(Incoming call via SIP Trunk) same=>n,Verbose(${CALLERID(num):0:3}) same=>n,GotoIf(["${CALLERID(num):0:3}" != "263"]?:noCCatstart) same=>n,Set(CALLERID(num)=0${CALLERID(num):3}) same=>n,Verbose(a CallerID is ${CALLERID(num)}) same=>n(noCCatstart),Verbose(b CallerID is ${CALLERID(num)}) ; This is the freepbx IVR we used to handle incoming calls. Change to whatever is in use on your environment. (extension/queue/etc) same=>n,Goto(ivr-3,s,1) same=>n,Hangup()