Исправлено.
В extensions_override_freepbx.conf изменил блок
[func-apply-sipheaders]
include => func-apply-sipheaders-custom
exten => s,1,Noop(Applying SIP Headers to channel)
exten => s,n,Set(FROM_DID1=${FROM_DID})
exten => s,n,ExecIf($[${LEN(${FROM_DID})}=6]?Set(FROM_DID1=8111${FROM_DID ...

