There is a way to save hundreds of pounds a year on your mobile-phone bill, and flog any upgrade you get to earn some extra in cash on top. It is all about taking advantage of mobile-phone companies’ desire to keep your custom. They will throw serious cash at anyone who threatens to leave their network. But you have to push to get the best deals. If you are close to the end of your mobile-phone contact, call up your network and ask what deals are available. Often, they will just offer you their standard list of accessible tariffs. Refuse this and tell them that the deal is so bad you are willing to disconnect. You will then be put through to the customer- retention department. Ask for a better deal and, usually, you will be given a range of “hidden tariffs” available only to those connected to this line. You will also be offered a handset upgrade, which you should definitely take and then sell on eBay for up to £300. Check which handsets will sell for the most before making your decision.