Digital Data, Analog Signal

{ A cos(2pfct)
s(t) = 0

{ A cos(2p(fc + d)t)
s(t) = A cos(2p(fc- d)t)

On voice-grade line is typically used up to 1200 bps.
On radio is used in the range 3-30 MHz
On local area with coaxial cables it can be used with higher frequencies.
A voice-grade line uses frequencies in the range of 300-3400 Hz To achieve full-duplex transmission, the bandwidth can be split ted at 1700 Hz.
Frequencies centered on 1200 Hz and 2200 Hz may be used for representing binary digits through frequency shifts of 100 Hz.

A two-phase system may use a shift in phase to represent the value 1, and no shift in phase to represent the digit 0.

{ Acos(2pfct +p)
s(t) = Acos(2pfct)

The frequency f_c depends on the carrier. it is not part of the encoding scheme.
With smaller phase shifts more bits can be represented. In particular, quadrature phase-shift keying (QPSK) represents two bits.
Each angle can get more than one amplitude. In particular, a standard 9600 bps modem uses 12 angles, four of which have two amplitude values.
It is not difficult to extend the encoding to cover more bits, but with that comes a requirement for a more complex hardware.