AT&T customers will now have to wait a bit longer to get an upgrade, as the carrier just revised its upgrade eligibility policy.

Following in Verizon Wireless' footsteps, AT&T announced it has extended the wait period for customers to be eligible for a new upgrade. AT&T customers previously had to wait a minimum of 20 months before they could upgrade their devices, but now that period extends to a full 24 months. The change applies to both new and existing customers whose contract expires next year or later, but not to Corporate Responsible Users with contractual upgrade terms.

"Today, we're announcing a 24-month upgrade policy across all of AT&T's wireless products and services," the company announced in a blog post on Sunday, June 9. "This aligns device upgrade eligibility with our standard two-year wireless agreement and it applies to any customer whose agreement expires in March 2014 or later."

Both AT&T's and Verizon's upgrade policy changes will take effect over roughly the same time frame. The Big Red is implementing this change for contracts starting in January 2014, with AT&T to follow a couple of months later.

The larger carriers enjoy massive customer bases because consumers want to get the latest and hottest mobile devices, but for a more affordable, subsidized price. Paying the full cost of a high-end device up-front is too big of an investment for most, so they choose to sign two-year agreements with carriers to get devices for a lower up-front cost. Carriers, meanwhile, recoup the subsidies over the span of the contract. As competition is rapidly heating up in the wireless segment, however, carriers try their best to ensure their customers stay tied with them for as long as possible.

Extending the wait period between upgrades from 20 to 24 months may not seem like much for consumers, but it will definitely count for carriers. Customers will also be eligible for a partial discount off a device's normal retail price after completing six months of a contract, but they have to commit to a new two-year contract. Those who want to avoid the two-year agreement must pay the full retail price to purchase the device.