Sorry you had to lose your phone like this. I always keep my phone in my pocket, but it's a piece of crap, so I'm not too bothered about it.
My friend had his iPhone snagged at an Arctic Monkeys concert, so never keep your phone in your pocket! Another fan from the Czech Republic who was with us lost his entire bag, with his Mac Book in.
I've always been particularly lucky, or it's just because I'm from Liverpool and know what I'm doing. I did try and get my purse taken away from me at the hostel, but I knew exactly what the guy was doing, because he was trying to distract me by getting me to give him my number on his obviously stolen BlackBerry. The screen was cracked and the phone had just been disabled so he couldn't access it. He was also telling me this shady story about how his uncle had kicked him out so he had to stay in a hostel. They get you first by asking you for directions to seem like friendly tourists.
Dudes, London isn't a very jolly place, and although my bag doesn't zip up, I understand the need for it. Check where your things are regularly!