There's no sense in releasing a quad-band phone if it's locked - you wouldn't be using more than a single band most likely. Being tied in to a contract means Cingular gets your money - they don't need the phone keeping you there. Apple wouldn't have an interest in locking it for the first reason I gave (you couldn't use it to swap out to a different or prepaid SIM when traveling in areas that use other GSM bands, like Europe).

Interesting will be what kinds of partnerships they make in other countries. Apple is launching in the US first, but the product is obviously intended to be a global one - another reason for a soft keyboard rather than using a fixed qwerty design.