Verizon customers will have to wait longer before being able to upgrade, as the wait period on device upgrades is now a full two years.

The nation's largest carrier just announced it is making some changes to its upgrade service. Up until now, although Verizon customers signed two-year contracts when purchasing a subsidized phone, they were able to get an upgrade after 20 months. Verizon is now extending that wait period on device upgrades to 24 months, which means that customers will not have to wait a full two years before being able to upgrade.

"In alignment with the terms of the contract, customers on a two-year agreement will be eligible for an upgrade at 24 months vs. today's early upgrade eligibility at 20 months," explains the carrier. "This change aligns the upgrade date with the contract end date and is consistent with how the majority of customers purchase new phones today. The first customers impacted by this change are customers whose contracts expire in January 2014. As always, customers may purchase a new phone at the full retail price at any time."

As Apple Insider points out, Verizon's announcement also hints that its New Every Two program, which gave customers a $30 or $50 credit toward a new phone, is coming to a full end. While the program theoretically ended back in January 2011, Verizon still allowed subscribers to use their expired credits. As of Monday, April 15, that's officially history.

The carrier further explains that customers can still share upgrades on accounts, provided that those upgrades are within the same device category. In other words, customers can upgrade a feature phone to a smartphone, or a basic tablet to a more high-end tablet, but cannot use a smartphone's upgrade to get a new tablet, or vice versa.

Verizon's announcement on Friday, Apr. 12, gave no reason for the changes. Rival carriers AT&T and Sprint, meanwhile, seem to be maintaining their 20-month upgrade interval at least for now. As the nation's largest carrier, Verizon sold 6.2 million iPhones in the fourth quarter and saw record numbers in terms of smartphone adoption. Over the course of 2012, the carrier gained as many as 5 million new subscribers.