Apple has begun to offer the iPhone 3G without a contract in its own retail stores, according to a new report. The move comes just one week after AT&T confirmed that it would offer the handset without a contract. Apple Insider reports that the two companies differ on the terms of sale, with AT&T restricting units to one per customer, who must have an existing AT&T contract, while Apple is not requiring either pre-requisite. The no-contract…