It's available as software-only for use with a compatible USB-equipped transmitter including the SpektrumT NX6 to NX20 - or the Spektrum InterLink?. It's also available with the Spektrum WS2000 USB Dongle that's compatible with Spektrum 2.4GHz DSMX/DSM2 equipped transmitters, like the DXS transmitter included with many of the most popular Ready-To-Fly (RTF) trainer aircraft, for wireless operation.
eBay