I've been investigating this for a while now since although I do have a phone with rsap and a Three One Plan with unlimited data plan, I'm finding that my phone drops the connection occasionally and won't reconnect (Samsung Galaxy Note 3)
I intend to use the data for traffic only and have checked usage over a month or so (around London 5 days a week commuting) and also wifi hotspot with my phone connected and running Waze. Total usage works out at about 10MB per week.
So I've tried a 3 pre paid 1gb sim but at 6 pounds lasting 30 days, this is overkill and I'd rather have something with better reception for when I drive outside urban areas (I find that Three is pretty bad for this).
So penny pinching me had a bit of a further search...
I've bought a few PAYG Sims from EE (ebay EE shop) which are £1 each and include £5 credit preloaded using their 7 day 50mins calls and 50 text pack. You can then place it in a phone (with mobile data disabled before insertion to prevent initial usage of and data - very important step). Text 150 with "STOP PACK" which disables the initial preloaded pack leaving you with £5 credit. You then text to start the £1 data bundle with gives you 100MB data lasting 7 days and auto reoccurs each week. Just simply then insert into the SIM slot and it will automatically find the APN settings and has effectively given me sufficient data for traffic usage lasting 5 weeks for £1!
Going one step further, but with minimal extra faff, I have found the People's Operator PAYG SIM who run off the EE network. If you sign up via some websites (google ken's tech tips) you get £10 free credit and do not have to provide your credit card details. Their PAYG tariff is 1p per MB for data which means the £10 should easily last me the 3 month duration at which they will disconnect me if I don't top up. I will review what I do at that point but I'll take 3 months for free for the moment thanks! One minor thing though is that when you insert the SIM it picks up it is an Orange SIM. You can easily go into the MMI and change the APN setting for the host (details are on the (People operator website).
So those are my tips: TPO which should give you either 3 months free then around £3.33 per month if you want to continue (since minimum top up is £10 I believe)
Or £1 per 5 weeks via EE throwing the SIM away and activating a new one every 5th Sunday evening. Note they will only send 2 SIMs per household in a 3 month period, so you will need a mate to get an extra pack to tied you over
