toofy, ok there are still the points:
– did MS dial both calls (outgoing)
– did MS dial one call (outgoing) and other call is incoming
– did MS receive both calls (incoming)
I looked at Call Waiting (GSM0383) as MS needs notification that a call is there to know to answer it. Also Call Hold (GSM0383) would be relevant as you say no multiparty (conference call) in progress (GSM0384)
As dual call appear to be supplementary services there is a trade of information between HLR and VLR. As one call is already in progress it would appear the second call would be route through same Mast as the one currently handling call. There appear no PCH required as HLR and VLR know where MS user located.
What I have not found out yet is where additional assignment (GSM0408) is sent on FACCH or SACCH etc…