By Slash Lane

Published: 07:50 AM EST (04:50 AM PST)

A calendar listing for San Francisco's Moscone Center has led to speculation that Apple's annual Worldwide Developer's Conference will coincide with the three-year anniversary of the original iPhone's launch.

The Moscone Center Calendar lists a "Corporate Event" from June 28, 2010 through July 2, 2010 in the Moscone West hall. Previous Apple events have been reserved with the same title.

This year, WWDC 2009 ran June 8 through June 12. In previous years, the event has marked the introduction of new iPhone models. This June, Apple introduced the iPhone 3GS.

The original iPhone debuted on June 29, 2007, along with an exclusive contract with carrier AT&T. Since then, it has been rumored that the two parties are locked into a three-year deal due to expire next summer. While AT&T has reportedly attempted to extend that contract, rumors have persisted that Apple will expand to other carriers.

If WWDC 2010 does take place on June 28, 2010, it could be booked to coincide with the expiration of the current contract with AT&T. Recent reports have suggested that Verizon, the largest wireless carrier in the U.S., could offer a CDMA compatible iPhone next year. Some analysts see Verizon as the best choice for Apple to expand the platform, but others feel technical limitations and different corporate styles could serve as a roadblock for such a deal.

For their part, Verizon officials said last week that their network would be capable of handling the added bandwidth from the addition of the iPhone. They did not, however, imply that the handset was coming to their network.

Another option could be T-Mobile. While the fourth-largest carrier in the U.S. does not have the size or stature of AT&T or Verizon, it is a GSM-based network, meaning compatibility with T-Mobile would be simple to accomplish with the existing iPhone hardware. Given the simplicity of such a move, some have predicted it to happen in 2010.