For a long time, Apple and their flagship iPhone were on top of the world, keeping a stranglehold on the smartphone market with a quality product and numerous carriers happy to sell it. But iPhone sales have declined recently in the face of improved Android products. Earlier this year, Samsung’s Galaxy S4 surpassed the iPhone 5 as the most popular phone on the market, and according to a report published by Moffett Research on Thursday, the shrinking sales figures don’t just spell trouble for Apple, but for their network carriers as well.

In this case, Verizon Wireless is the phone network that has found itself in deep water. After the iPhone’s booming formative years, Verizon signed a hefty three-year contract with Apple that promised a total of $40 to $45 billion in sales of iPhones and other products. Since the contract terms began in 2011, Verizon has struggled to meet those numbers. Based on the first two years of the contract, Verizon is still holding $23.5 billion in leftover “purchase commitments”–a substantial figure that more than doubles their net iPhone sales from 2012. In other words, Verizon is facing a near-insurmountable deficit against their contract to Apple, and unless the smartphone market turns around dramatically and iPhones start flying off the shelves–something that could happen if Apple releases a new phone, but probably not to the level that Verizon needs it to–then the company could be forced to write a fat check when their contract expires at the end of the year.

Whether or not Apple will actually make Verizon pay up on their failed commitments–referred to technically as “contractual shortfalls”–remains to be seen. In their report detailing Verizon’s difficult position, the Moffett Research firm theorized that it would be a mistake for Apple to force Verizon to write a check. Verizon’s total shortfall on the iPhone contract will likely equate to somewhere between $12 and $14 billion. If Apple forces the company to pay back every cent, they will not only squander their relationship with Verizon, but also advertise very publicly the under-performing nature of their iPhone line. Such an event would send stockholders jumping ship and leave other phone carriers questioning just how many iPhone units they will be able to move in coming years. After all, when Verizon signed that contract, the iPhone seemed like one of the safest bets in the world. Now, the tables have turned and analysts are asking whether or not Apple’s device has reached its limit.

In terms of the other carriers, both Spring and AT&T are in better shape than Verizon, but contractual outlook isn’t entirely sunny for them, either. Moffett Research reports that AT&T had $3.8 billion in iDevice shortfalls at the end of 2012, while Sprint also signed an Apple contract in 2011, but only promised $15.5 billion in sales. In addition, Sprint’s contractual terms give them four years to reach the commitment number, and with $6.4 billion of the goal accomplished thus far, the company should be able to satisfy the contract provided that the smartphone market continues to grow and Apple continues to be a major player.