A Three Data Reward SIM is a free SIM card on Three which comes with 200MB of free data each month. It's designed for use in devices which only require data such as mobile broadband devices and tablets.
Get 200 Mb per month free forever for your tablet without the need to ever top up your SIM. If you ever do use up this data then you can buy data for the rest of the month by making a one off payment. The smallest of these payments is £15 for an extra 2 Gb of data.