Oh I see I didn't noticed that until now! When I've seen that scene I've thought it's his own phone and not Hiura's. It was so quick I didn't paid enough attention on the numbers.
Yeah that makes it more probable he was killed by someone entrusted by the Supporter, or as Tamad mentioned in his theory, the Supporter himself, since he used all his money.
Believe it or not when I typed it in wikipedia, Johnny Mnemonic was the first thing crossed my mind too first. (I loved that film when I was a kid!)
However if I remember it correctly (I've seen it like about 10 years ago so don't take my word for it), but Johnny didn't particularly seemed like an irresponsible guy to me there. Actually it's the opposite, since he's entrusted with the thing (virus was it or something important) and he is responsible to deliver it. Of course it's entirely possible he might got the nickname from here, because that's cyberpunk too, and we've seen plenty of cyberpunk reference already (Ghost in the Shell mostly).
I'm not entirely 100% sure his nickname (if Johnny is indeed a nickname and my theory is right about that) would come from a film though, but it is certainly possible for now.
Well yeah Johnny Depp could play his role genuinely, if they ever going to make a Live film adaptation.
Hmm. after a quick google search:
Johnny Boy who is quite an irresponsible fellow in a mafia film called
Mean Streets, 1973. Another interesting thing: Played by Robert De Niro who was also the protagonist of the first film Eden of the East mentioned: Taxi Driver.