That Apple gets a cut of the monthly subscriber love from AT&T is common knowledge, but neither party has been too keen to share the exact details of just how much of your iPhone rental passes straight through the carrier’s fingers and into Cupertino’s coffers.  Now, thanks to an obscure rule regarding “deferred revenue” – basically when one company promises to pay another at some point in the future – Apple has been forced to reveal how much it expects to receive once it has finished holding AT&T by the ankles and shaking them upside-down.  It’s a figure that has surprised even jaded analysts: on average, $18 a month or $432 in the space of a two year contract.

Of course, the key here is “average”: Apple is under no obligation to disclose to the Financial Accounting Standards Board exactly how different customer circumstances affect the amount they receive.  For instance, bringing a new subscriber to AT&T might net them a higher figure, say, than an existing customer switching handsets to the iPhone, and the value of the monthly plan is likely to have a similar impact.

Comically-named Gene Munster, the analyst at Piper Jaffray who spent the time hammering away at his calculator, professed no small amount of surprise at the $18 figure; he has previously estimated Apple’s return on each iPhone at around the $6.50 mark.  He has predicted that, after two years, the cellphone will drop to around he $300-retail point, at which time Apple will be making roughly $9 per month from AT&T.  Still, it’s an impressive deal and one which further indicates the unlikelihood of an unlocked iPhone being available any time soon.