Now that Phones4u is no more, Carphone Warehouse is one of the few independent retailers selling mobile phone contracts in the UK. With mounting competition from dedicated carrier stores, the company hopes to stand apart by offering its customers better impartial advice. To that end it's teamed up with RootMetrics, a firm that specialises in monitoring mobile network performance. Using its CoverageMap app, which combines professional and crowdsourced network tests, Carphone Warehouse staff will now tell shoppers which carriers offer the best coverage in their local area. Whether you're interested in call quality or download speeds, this information could save you from picking a weak network. You can always download the app for yourself or check RootMetrics' map online, but a timely reminder just before you sign up for a new contract can't hurt.