People will scoff and say "Yeah, but all kinds of companies have internal firewalls, big deal". But no, these were literal walls that would appear over a weekend and suddenly part of the campus was off-limits to those not on the iPhone project.
I found it in Fred Vogelstein's "Dogfight: How Apple and Google Went to War and Started a Revolution" [0]. Decent read, not amazing IMO, but with fun tidbits about the iPhone / Android launches
Any book about the development of the iphone or articles in the business press from a few months after product introduction (if any are still online…try Fortune).