EDIT (20/6/16): Multiple other options exist to get Giffgaff SIMs for free apart from the one I mentioned in this article
The problem with sim cards is that the time you need them the most is the time you can’t get them yet. Like when you first land and want to use Uber, or check out directions to your hotel, or send your parents a whatsapp to let them know you go there safely. Until you can find wifi, you’re helpless. So the gold standard is to get a sim card and have it activated before you reach your destination, so you have data from the get-go. Of course the issue is that you’d (1) need to find someone who is willing to ship you a sim card and (2) the price of shipping might negate any cost savings.
I’m going to the UK and France this August (and looking forward to writing my very first (and probably very last) SQ Suites report) and have been looking out for cheap calling and data options.
I’ve been told that GiffGaff is one of the better options there. It’s a VMNO which runs on the O2 network, and they offer some quite nifty plans- see below. The 10 pound plan sounds like the best value to me, but that of course depends how long you intend to be in the UK.
Giffgaff has a referral program that means when you activate a sim card sent to you by someone else, that person earns a bonus too. This has led to a cottage industry of sorts on hardwarezone where people openly offer to send you free sim cards, in anticipation that they’ll earn some credit when you sign up. Oh, and you also get an extra 5 pounds free credit when you sign up using this route. Meaning that if you pick the 10 pound per month plan, you pay 10 pounds, get that plan plus an extra 5 pounds of credit (Which can be used after you’ve exhausted your data or minutes in the 10 pound plan)
I’ve tried one such service – email@example.com. My sim cards arrived promptly 2-3 days later with a nice note attached
I’d strongly recommend this service to anyone who is going to the UK. You can get nano, micro, standard sim cards, and as many as you want (Although, for common decency reasons, you shouldn’t horde them)
Now if only I could find something similar for France…