~~~ UPDATE ~~~
Just spoke to a call centre (India, I think) and the girl arranged to ship me a brand new OMC out tomorrow, and even let me choose a delivery slot; most impressed. I then asked her how I'd go about getting the unlock code for my replacement
OMC when it arrives, and her reply baffled me slightly: "Oh, don't worry Sir: they unlock the replacement handsets before they are shipped out to you, so it will be unlocked when it arrives"...
Righttttt... (but she was extremely quick and polite with the replacement, I don't do telephone anger; she's just doing a badly paid job)
Next step, I called back (I think I got the Phillipines this time, and a sweet sounding girl) and I explained that the previous adviser had informed me that the replacement
OMC would arrive pre-unlocked, to which she said "No Sir, I've never heard of that being the case; ALL handsets are locked" (which I had gathered already). After slowly and politely stating my case, that I'd been told by the previous adviser, to the contrary, she said she'd put notes on my account, and that when I get the replacement OMC, they'll try and apply for the unlock code, and I'll get it as a complimentary gesture... we'll see, hey!
They're VERY efficient! I can't see where all the other complaints come from; you just have to be patient, calm and polite. Simple.