iPhone... iDon't understand what they're up to? [Brit]

I noted with interest this story on El Reg that AT&T have apparently called in the legal dogs on a company about to release software that will allow iPhone users to connect to any mobile network operator. In case you're wondering why this should be such a big deal, the iPhone shipped with a catch - you had to use AT&T as your carrier, or you couldn't use the phone... which is absolutely ludicrous in the highly commoditised mobile phone market.

Of course, it didn't take long before this act of abject stupidity was run through the gamut of hackers and interested parties with various solutions providing an unlocked iPhone appearing online within weeks of its retail release.

I'm gobsmacked at Apple/AT&T's tie-up decision here; the universe of people prepared to a) fork out for a hugely expensive phone and b) potentially shift everything into AT&T from a current provider can only be a small one... with new phones being released all the time, consumer choice is one thing this particular industry isn't short of.

So genuinely, I'm interested in the reasons behind their initial decision making process - now that you can unlock your iPhone with a couple of corks, two pins and a few hours of your time (as an example of the lower end of the unlocking solution spectrum) it really is game over for the likes of AT&T if they see their future in such restrictive tie-ups.

Can someone perhaps explain a cunning plan that I've completely missed here?