Are you the kind of person that uses every available bit of inclusive credit on your mobile phone contract each month. Well, this doesn't apply to you. But for the rest of us, we are apparently wasting £800 million each year on mobile deals unnecessarily.The research undertaken by Top10.com indicates that pretty much all of that is down to choice of contract, with 55 per cent of the 2000 people surveyed not using all of their allocated monthly minutes. Stepping down to a lower tariff would mean saving cash, collectively that £800 million figure. Makes you think, doesn't it?For some (42 per cent), tariffs are just too confusing, while 46 per cent claim they worry about being on the wrong tariff and were being overcharged. At the other extreme, 8 per cent have to top up their bills because they go over their limits - and we all know how expensive that can be.According to Alex Buttle of Top10.com: 'With so many mobile phone contracts available, it’s no surprise that so many people find tariffs confusing. But it’s worrying that so many people are wasting money every month because they don’t change their tariff to match their level of usage.''Before people upgrade their phones or switch networks, we recommend they check their previous bills to work out how many minutes they’re actually using. This is even more important now that new devices like the iPhone and HTC smartphones come with long contracts, generally lasting 24 months. Making the right contract choice is just as important as picking the right phone.'