Verizon Communications is offering subscribers who trade in an old iPhone a free iPhone 6 for a two-year contract.

The largest wireless carrier in the U.S. made the announcement just hours after Apple debuted its anticipated new iPhone device.

The announcement also comes as some critics have speculated that the newest iPhone, starting at $199 with a two-year contract, wouldn't be able to be competitive as other carriers eliminate contracts and unbundle service charges from the cost of devices, according to Reuters.

Customers who trade in an iPhone 4, 4s, 5, 5c, or 5s in working condition will receive a $200 gift card that can be applied to the regular $199.99 price for the basic 16-gigabyte version of the iPhone 6, according to Verizon's website.

The offer does not apply to Apple's other new phone, the larger iPhone 6 Plus, however.

Verizon has been reluctant to dive into equipment financing, and its promotion indicates its "attachment to the older contract model," which locks subscribers to the company for a fixed term, said Jan Dawson, analyst at JackDaw Research to Reuters.

"There is an inherent risk in the shift to installment billing that it creates more loyalty to the device than to the carrier," said Dawson. "Verizon sees the value of the two-year contract in that tying a device to a two-year plan can prevent churn."

He noted that new device releases are often major factors for subscribers in deciding whether to switch carriers or not.

Carriers have been competing aggressively for subscribers as the market for new device customers shrinks by slashing prices and creating unique promotions to steal each other's' customers.

T-Mobile announced after the new iPhones were released that it would beat any other major carriers' trade-in rates and give customers a $50 credit.

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