The software allows owners to get access to the operating system and system software protected as firmware on the phones and allow them to modify both to their hearts' content.

Most carriers lock down the operating system to keep customers from messing around with the OS, partly to reduce support costs and keep the phones' links to the cell network from being corrupted, but also to keep customers from adding software or services from third-party developers that the carriers would prefer to supply themselves -- at a premium price.

Unlocked phones and user-installed software pose much higher risk of infection by malware or corruption of system software. Most bootloader unlock apps include either a method or reminder to users to back up system images of the phones to restore them more easily if necessary.

HTC views unlocked OSes as a way to encourage both ISVs and owners to get more involved developing apps and mods for the phones, according to an interview in the WSJ with HTC CEO Peter Chou.

HTC did investigate whether it should build its own operating system to compete with Android, as Samsung has done.