Apple’s contract differs with every carrier that sells the iPhone. Such sales accounted for 56 percent of Apple’s $55 billion in revenue last quarter. In most cases, Apple sets a quota for how many iPhones the carrier needs to sell over a set period of time, usually three years. If it does not agree to the quotas, it does not receive the iPhone.
If quotas are not met, the carrier is obligated to pay Apple for unsold devices, according to one person who negotiated with Apple while at a European carrier.
Note that harm to competitors is not harm to competition. Indeed, the marketing requirements can be viewed as a simple, direct way to better align the incentives of carriers with the profitability goals of the manufacturer. Often retailers invest less than manufacturers would prefer, and the contract could be one way of addressing this incentive conflict....Apple’s competitors complain that the big purchases Apple requires from carriers strongly pressure them to devote most of their marketing budgets to the iPhone, leaving little money to promote competing devices, said an executive at one of Apple’s rivals, who declined to be named to avoid jeopardizing carrier relationships.
There is also the possibility that the carriers are using the threat of antitrust to re-negotiate their contracts so they can make themselves better off, but often at a cost to competition (see my paper on a related topic). Remember that parties cannot contract around inefficient antitrust rules. The right to sue to void an anti-competitive contract is an inalienable right.