Since I unlocked my iPhone last week, various friends have asked me if it is, indeed, legal. My impression was always that it technically wasn’t under the DMCA, but I was heartened when I found this exemption ruling from late last year:
The Librarian of Congress, on the recommendation of the Register of Copyrights, has announced the classes of works subject to the exemption from the prohibition against circumvention of technological measures that control access to copyrighted works. Persons making noninfringing uses of the following six classes of works will not be subject to the prohibition against circumventing access controls (17 U.S.C. § 1201(a)(1)) during the next three years.
. . .
5. Computer programs in the form of firmware that enable wireless telephone handsets to connect to a wireless telephone communication network, when circumvention is accomplished for the sole purpose of lawfully connecting to a wireless telephone communication network.
I’m no legal expert, but it would seem that using a program to unlock your phone is indeed legal. Whether or not it’s legal to sell said software may be another story.