We just setup a CCME.
For each ephone, we define 4 ephone-dn like this :
number xxx secondary zzzzzzzzz
call-forward noan aaa timeout 20
But we would that the call forward is only fired for the external callers. If we make internal calls, we don't we to be forwarded.
And if possible, we want to keep or dn like that (internal number secondary external)