I have just come across one of these, basically you get a simcard with 200 min, 200 texts, 200 mb with no monthly charge at all.
*You have to pay a one off charge of £7.97 which consists of £4.99 for sim card, £0.99 activation fee and £1.99 for shipping.*
Edit you can buy this from Amazon and eBay for 0.99p
Runs off of three.
I have just noticed you can also buy the sim cards off ebay for 0.99p
Only works with android or apple.