A former analyst at Sanford C. Bernstein has calculated that Verizon Wireless could end up owing Apple as much as $14 billion by overestimating projected iPhone sales.

Craig Moffett, who now heads up Moffett Research, points to a multi-year deal that Verizon Wireless signed with Apple in 2010. Under that arrangement, he says, the operator is obligated to purchase $23.5 billion of iPhones in 2013 alone.

Given the size of commitment is more than double what Verizon Wireless sold in 2012, Moffett reckons the biggest operator in the US may have a shortfall of between $12 billion to $14 billion.

Bloomberg contacted spokespeople from Apple and Verizon Wireless but received no comment from either about the operator’s iPhone purchase commitments.