What is the "proper" way to treat a "no charge" mark?

[jcastro@xxxxxxxxxxxxxx (Juan Carlos Castro y Castro)]

If I make a call to an SS7 number and the ACM/ANM I get back have a "no 
charge" mark, I'm treating this as "early media", i.e., I don't forward 
an OK to the SIP side, only a session progress. (I did a patch to 
chan_ss7 for that.) Eventually, when the call ends, I will have to 
forward a 4xx or 5xx or 6xx return code to the SIP side. What should be 
the correct code to forward? Or am I treating this completely wrong?

Juan