Are you sure that you want to do this using DTMF and DTMF only ?
If short-messages (SMS's) are an option, or likely necessary then the DTMF route is unnecessary.
Unless your control circuitry is hooked up to your wired / fixed-line phone line, you'd need something called a GSM module to send/receive anything (voice, SMS...). Once you have such a module in place, you can interact between the module and your microcontroller using something called AT-command set. If DTMF is necessary in this situation, I am afraid your best bet may still be the dedicated DTMF decoders, and DSP route may be unnecessary or more complicated than it has to be.
If you do want to hit the DSP route, do check out Cortex-M4 microcontrollers, available from TI, Freescale, ST, NXP. Many of the silicon vendors might even supply DTMF detection library.
The advantage of the SMS route is that you do not need the DTMF detection capabilities.
BTW, DTMF detection can be done on a lot more lower-powered MCU, which do not require full FFT implementation but use some simplifications or alternative like Goertzel's algorithm, which are good enough for detecting presence of certain frequencies, as is the case with DTMF.
Find more information on the software (general MCU, non DSP) approach here: