Speaking of contacting Luca...
During the scene where Sonny, Tom, et al are trying to locate Luca, someone suggests he shacked up with the "broad" and they tell Michael to try him there. Michael just picks up the phhone and starts dialing. How does Michael know the "broad's" phone number?
Actually, they make a point of saying that Luca would never stay at a broad's place. Michael is presumably calling Luca at home. Although it could be argued that it's unlikely that Michael would know that number, either.
From J Goeff's transcript:
TOM
Has anyone been able to get in touch with Luca?
CLEMENZA
Eh, I've been trying all night. He might be shacked up.
SONNY
Hey, Mick, do me a favor --
TOM (background, to Clemenza)
Luca never sleeps over with a broad -- he always goes home when he's through...
SONNY (to Michael)
-- try ringing him...