I'll be buying a sim card to use in my unlocked phone in London next month. Can I expect my UK number to be active when I leave the shop?
Yes, you can.
Yes. You can even test it while in the shop and ask for any assistance if needed.
We're going to do this too. I've already purchased two unlocked phones to bring with us to London this fall. Anyone have a recommendation on which shop to buy the SIM card from? Is just any OK to pick up from Boots? I imagine that it's a lot easier to just go to a mobile phone shop and have someone help you out to get it working before leaving the shop.
I'd recommend going to one of the shops run by one of the carriers, especially if you're bringing your own phones. I've had good experience with T-Mobile, but I think any of the others would work, too.
I saw there is an "Orange" shop near our apartment, will probably go there. Seems most rates are 20p per minute (Orange and T-Mobile). Sure beats $1.99/min with our US based phones in London!!