There is a new xceiver called "CM8880 DTMF" that may fit your needs. Not sure
who makes it, but I bought one from Scott Edwards along with some insights for
it's use.

Scott Edwards
520-459-4802
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Subject: DTMF tone detection with PIC
From:    stephnss%PYROTECHNICS.COM@prdnet.polaroid.com at INET
Date:    11/9/95  4:23 PM

I was wondering if anyone has used a PIC to detect dtmf. A method that comes
to mind would be to generate all the individual tones with timers based on
the RTCC/TMR0, and then compare the unknown DTMF squarewave input using an
XOR instruction to the individual tones. Any other idea's or methods?