Prepaid mobile carrier has around 5.3 million subscribers.
U.S. prepaid carrier Leap Wireless could be left with as much as $100 million worth of unsold iPhone units.
The firm, which operates Cricket Wireless, told the Wall Street Journal that it's considerably behind in its prepaid iPhone sales. When it completes its year-long contract with Apple in June, it's likely to have sold half of the iPhone units it committed to selling.
Apple partners with prepaid carriers in an effort to attract more lower-income consumers. Leap currently has around 5.3 million subscribers but is affected by the fact that it has less network access than America's major carriers.
With Leap's no-contract plan, consumers pay nearly full price for the iPhone but are then charged a lower amount for monthly payments when compared to carriers that require two-year contracts. By paying Apple a small subsidy, Leap offers the iPhone 5 for $500, which is around $150 less than buying the smartphone from Apple itself.