By Harriet Morphy-Morris Opting for a SIM-only deal has long been a tested way to get bigger amounts of data for a fraction of the price, not to mention you have better flexibility the next time you upgrade your phone. The latest deal from iD Mobile will give mobile users a chunk of data, EU roaming data, unlimited minutes and texts all for less than £5 a month. Shoppers will also be able to claim cashback off their contract each month, a total that adds up to a huge £108 over the course of the 24-month deal. It can be found on Mobiles.co.uk, on its 54GB a month plan that’s now just £4.50 a mo…