I've just got a Sony Ericsson J300i and I was doing a some reading up on
the various attachments and accessories. I have a data cable for it
(DCU-11, a third party one by Dr. Cable), but I noticed there's an
"unlocking cable" that's needed for removing restrictions.

What's the difference between that and the DCU-11? I assume that it must
be wired differently somehow, but I can't understand why -- other than the
obvious one of extracting extra money out of people. I mean, the cable is
just converting USB -> serial isn't it, and the unlock is done by sending
certain data to the phone?

See More: Sony Ericsson unlocking cable