I would recommend that you consider using a M8870 rather than a SSI202.
(this is a DTMF decoder, for those who don't know).  The M8870 is less
likely to give a false decode on noise or voice.  This part is available
from Mitel and Teltone, and you can find data on Mitel's web site....

Jeff
At 04:26 AM 5/17/97 -0400, you wrote:
>Data on this device is available in the June 97 ELEKTOR including an
>application circuit.
>
>Steve.....
>
Jeff Otterson
-------------
otterson@mindspring.com
Maker and user of tools
PGP key available at http://www.mindspring.com/~otterson/pgp.htm