I have my iPhone officially unlocked by O2. However, today I had to unlock it unofficially too — naturally, using blackra1n + blacksn0w combination (I've donated for blackra1n once, and now I feel like I need to donate for using blacksn0w — it was my most painless jailbreak and unlock ever). You can ask, why did I do that?
Well, how'd you like a reason: when I swap my SIM cards I am not necessarily at my home iMac so I can connect iPhone to iTunes to do an iActiva..damn, just to activate it! I don't want it, really — it's nowhere simple and counterintuitive like hell: I've activated it already once, and I've unlocked it once — why should I bother doing it every now and then? So I had my iPhone blackra1n'ed, installed blacksn0w — whoa! It turns out, swapping SIM cards could be just that — swapping SIM cards. And this is the way it supposed to work.