It is very easy if you use a chip like MT8870 DTMF receiver or if you want to construct DTMF signal use MT8880 or MT8880 DTMF Transceiver. By using these chip, DTMF signal is converted to BCD (Binary) format (4 bit data). All chips mentioned here are MITEL product (www.mitel.com).

Hope it is useful for you.