Unlock your iPhone?

Walking around Cannes I came across a cell phone store advertising unlocking services for GSM phones and iPhones. One might think that's illegal, but it isn't and this store is located on a main thoroughfare, right across from a police station. (For those unfamiliar with "locked" cell phones: mobile operators typically subsidize phones and to guard their investment lock the devices to their networks. The phones can typically be unlocked by entering special codes or tweaking the memory, a service provided by the unlock shops.)