EBay's electronics buyback service will purchase several smart phone models for a guaranteed $200 over the next two weeks. The move comes as Verizon Wireless prepares to start selling Apple's iPhone online on Wednesday and in stores on Thursday.

Under the promotion, Instant Sale will pay $200 for a functional iPhone 3GS, Droid X, Evo 4G or Galaxy S Vibrant. This is the same price Verizon will charge for the 16-gigabyte iPhone with a two-year wireless service contract.

EBay says Instant Sale will also offer $200 to $450 for an iPhone 4 from AT&T Inc. Since its 2007 launch, AT&T has been the only U.S. iPhone carrier.

Verizon said it received record sales when it briefly began offering the iPhone to current subscribers last week.