By Sumner Lemon, IDG News Service

Efforts to unlock Apple's iPhone continued on Monday, with hackers claiming "very significant progress."

The locked iPhone only works with AT&T's EDGE network, and cannot be used with cellular service from other providers. Locked phones are generally used to help operators recoup the cost of subsidizing handsets for their customers, but AT&T is not subsidizing the iPhone, which is priced at either $499 or $599, depending on the model. Instead, the phone is locked because AT&T has a five-year agreement with Apple to be the sole iPhone provider in the U.S.

Unlocking the iPhone would be a boon for users locked into a contract with another U.S. carrier, or for users outside the U.S. who want an iPhone. While initial signs indicate an unlocked iPhone is possible, hackers must first overcome several challenges. One of those involves circumventing the authentication process in iTunes that both lets users register for an AT&T service plan and turn on the phone's features, including its camera and music player.

By Monday evening, U.S. time, hackers had made headway towards circumventing the activation process. But the phone remained locked at the time of writing.

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