In-flight Wi-Fi may sound like a great way to keep in touch with friends and family or catch up on work, but services are often so slow, you're better off sticking to the in-flight magazine. New satellite-based Wi-Fi services promise to change that, prompting a grab for capacity and customers by companies such as Inmarsat Plc, Viasat Inc, Gogo Inc, Panasonic and Global Eagle Entertainment Inc. Wi-Fi on U.S. domestic routes is already widespread although air-to-ground technology can mean service is slow.