Verizon may end up owing Apple billions of dollars in 2013 due to a purchase commitment for iPhones, according to a report. Telecommunications analyst Craig Moffett estimates the carrier could have a shortfall of $12 billion to $14 billion, with Verizon obligated to buy $23.5 billion in iPhones this year; a second analyst concurs with the lower number. Such a shortfall could spark some negotiation between Verizon and Apple on how to fill the gap.…