Several sites like this one said they could supply an unlock code by email, so I decided to chance the £2.79, and waited (codes displayed "instantly", it said, though warned that "a small percentage of specialist codes take up to 24 hours"). 24 hours later, no codes, no nothing. 48 hours later, ditto. A more thorough reading of their T&Cs (which, yes, I should have done before paying) revealed that there are some even more specialist phones which they can't unlock, though they were happy to take the money for something they knew they didn't sell.
A bit more Googling (which again, I should have done before paying the money) suggested that unlocking the N95 was pretty tricky & involved getting down & dirty with a soldering iron. I don't even own a soldering iron, so that method was right out. All non-soldering methods involved having either specialist software or specialist bits of 'flashing' kit. So today I decided to go to a proper phone shop with an actual address (and probably soldering irons) and get the phone unlocked by professionals, even if it did cost more that way. I asked at one of the phone shops on Cornmarket (can't even remember which, they're all called something like ZOMGStaxOfCheapFonezBNWT4U) and asked them if they did unlocking. They didn't. "You want to go to Benny's," said the chap I'd asked, "you know, the newsagent, on St Aldates." I looked doubtful & asked if they really unlocked all phones, but he assured me they did.
Benny's had a flashing LED sign on the window saying "UNLOCKING" and a large poster claiming that they could unlock all "new Nokia phones", with big pictures of the N95 and even newer, shinier models. Promising. :-} The guy at the checkout (who, to be honest, didn't look like a phone-unlocking guru) said I'd have to wait 10 minutes for his son to come back; when the son arrived, he said the N95 was no problem but it'd be £25 ("you have to open them up, see"). I handed the phone over, at which point it took him about 30 seconds (and a small screwdriver) to reduce it to a heap of small plasticky pieces.
There followed some more fiddling about with electronics and software (all this taking place in a kind of back office half-hidden by stacks of crisps) which I couldn't really see because the phone-guy's friends were popping in and out, chatting to him, snacking, etc. (To be able to do that kind of fiddly stuff with the innards of phones at all is pretty impressive; to be able to do it one-handed while eating chocolate hobnobs with the other hand takes style.) 5 minutes later, he put the phone back together, switched it on... nothing happened. I tried not to look too obviously as though I was thinking "ARGH WHAT HAVE YOU DONE TO MY PHONE" as he took it apart again, tweaked something, put it back together, and bingo, Nokia startup sound, one unlocked phone. :-)
When I came to pay I realised I only had £24.70 in my wallet. "It's nothing," he said. I offered to get more cash out from the cashpoint next door ("if everybody cheated you out of 30p you'd be hundreds short!") but he looked me in the eye and said "Some things are more important than 30p, like, you know, friendship." "That's very kind of you," I said, and legged it with my newly-unfettered phone.
Now I just have to work out how to get the phone to make friends with the internet...