Three have some amazing SIM-only deals available over at their online store including a number that offer unlimited data.
One such deal is the 1 month rolling contract which gets you 200 minutes, 5,000 texts and unlimited mobile data for just £12.90. It's the perfect deal for those looking to avoid long term contracts, but don't want to incur the larger costs associated with Pay As You Go packages.
Those happy to commit to a 12 month contract can get an even better deal such as the "Ultimate Internet 600" tariff which gets you 600 minutes, 5,000 texts and unlimited data for £15.90 a month. While a whole host of other deals are available starting at just £6.90 a month.
The good news is that you can choose between a standard SIM, a micro-SIM and a nano-SIM which means that all modern smartphones and tablets are supported. 3G highly recommend the SIM-only route especially for those whose contract has expired.