In some markets, iPhones were bundled with a contract because networks had bidding wars for exclusivity.
From the PoV of someone working at the network and having the luck to talk with some pretty high up there people... the exclusivity was only for order in which networks got the phone. As in, present-day T-Mobile Poland made a bid to be the first network to have it - but it didn't have any kind of long exclusivity and was soon followed by Orange and Plus (the other two "main" networks). All networks had special iPhone "plans" and the phone wasn't available outside of them, and the only technical difference was that said plans ultimately got the very buggy Visual Voicemail server attached and probably triggered workarounds for call handling bugs.
The Apple tax on the phone bill itself, and making it unavailable outside of contract, were all on Apple. (I think for some time using one outside of approved contract even required jailbreaking, but I can't be sure).