Norman Gillaspie wrote:

> I believe the caller ID demod chips will fit the bill
> for the receiver there is probably a corresponding
> transmitter IC.

  Well, an XR2206 is specifically designed for this function, having a
sinewave output and a digital input which selects between two frequency
presets with phase coherence.  You need to tune it up with a frequency
counter, and it's not CMOS however so draws a few mA.  (It's very old!)

  Cheers,
        Paul B.