This excerpt taken from the AAPL 10-Q filed May 1, 2008.
The Company currently relies on exclusive cellular network carriers for iPhone in certain countries, including the U.S.
In certain countries, including the U.S., the Company has contracted with exclusive carriers to provide cellular network services for iPhone. If these carriers cannot successfully compete with other carriers in their markets for any reason, including but not limited to the quality and coverage of wireless voice and data services, performance and timely build-out of advanced wireless networks, and pricing and terms of end-user contracts, iPhone sales may be materially adversely affected. Because the Companys agreements require each carrier to make revenue-generating payments to the Company, a carriers non-performance under or termination of an agreement, or the carriers inability to attract and retain iPhone customers, could have a material adverse effect on the Companys financial condition and operating results. If, contrary to the Companys license agreements or product specifications, an iPhone is unlocked from an authorized carriers network, the Company would not receive payments related to that iPhone from such carrier, which could have a material adverse effect on the Companys financial condition and operating results. The Company may choose to enter into arrangements with carriers in other countries or regions, and the same risks described above also would apply to those arrangements.