The problem with using a pure sine wave to transmit data is that a sine wave continues forever, and has a bandwidth of 0 Hz. Unfortunately, with this waveform, you can transmit zero data, and it takes forever to reach the destination.

So, in practice, we use waveforms that are not pure sine waves, but are modulated (or changed) to add information to the original sine wave. The process of modulation means that the signal is no longer a pure sine wave, and it no longer has zero bandwidth, so it can carry information at a realistic and useful rate.

So we can support many different services on our shared radio spectrum, we also try to get the most data in the minimum bandwidth, a figure of merit called bps/Hz, or "Bits per Second (data speed)" per "Hertz (a measure of the radio spectrum used)".

There are many ways to modulate a signal, but one of the most common for digital transmission today is called Quadrature Amplitude Modulation, or QAM. This changes both the amplitude and the phase of the sine wave. US Digital TV uses 64-QAM, with 64 different combinations of phase and amplitude, carrying 6 bits per symbol.

See:

http://en.wikipedia.org/wiki/QAM_(television)