With 30 minutes before his flight and “excellent” signal strength for T-Mobile’s airport-wide hotspot, ZDNet’s David Berlind decided to charge some Wi-Fi time on his credit card. No sooner had he paid than the signal dropped to nil, leaving him unable to load a Web page or log onto his company network. When he called the company to get his money back, a less-than-helpful service rep refused to issue a refund.