>    I've got a different question concerning phone interfacing.
> How do you detect whether a phone is on or off hook without
> inserting a loop detect relay yet keeping this detection circuitry
> isolated from the rest of the PIC circuitry?

[1] Use a very sensitive voltage sensor to detect whether there is more than
    12 volts on the line.  If so, then nobody has their phone off-hook.  Note
    that you need to draw only a few microamps when detecting the voltage, so
    you may want to use a small transformer to power an op-amp which could
    then detect the phone line voltage.  The output from this amp is then
    either fed through an opto or back-fed through the transformer.

[2] As above, but use a battery to power the phone-line side of things.

[3] AC-couple yourself to the phone line and look for audio.