A Credit Suisse analyst downgraded Verizon on Thursday, saying he no longer believes rival AT&T Inc. will lose its exclusive deal to offer Apple's iPhone before 2011.

Jonathan Chaplin, an analyst with Credit Suisse, said he believes the wireless giant is likely to keep the device until sometime next year, making business more challenging for arch-rival Verizon Wireless.

Our analysis suggests that Apple will eventually sell the device at all carriers; however, there is a much greater probability that AT&T keeps exclusivity for another 12-18 months than investors realize, he wrote.

Chaplin also said his expectations for earnings-per-share growth at Verizon have come down due largely to disappointing wireline margin results.

Like many analysts, Chapin had previously thought that Verizon would begin offering the iPhone this year, but now believes that this will not happen.

Till now, many unconfirmed reports having been go around that Verizon Wireless will become the second U.S. carrier to offer Apple's iPhone that now many believe that this is true, although it has not confirmed yet by either company.

Meanwhile, analysts at Oppenheimer & Co. recently predicted that all of the top of U.S. carriers will be offering Apple's smartphone by the end of this year.

Apple Inc. and AT&T have not disclosed the length of their exclusive contract. However, Apple appeared to reaffirm its commitment to AT&T last month when it unveiled its iPad tablet computer, when it announced that the carrier will be the sole U.S. data provider for the device.