A Mitel MT8870 will give you 4 bit binary outputs and a data ready signal. The device contains the filters for the high and kw frequencies and decode @ < 100mV. I included thee data sheet and I've seen them on Ebay for $3 - $4.00. Much easier than devoting such a large piece of the code space for decoding... another note is that there are DTMF generators that use the same crystal... If you choose another time base only you could easily decode them. This was a common method for semi secure radio based remote control. I used it when building my first amateur radio repeater for shut down and phone patch control.
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MT8870.pdf (220 KB)