If you need to generate DTMF tones and have a Parallax Propeller chip handy, there’s an object for that! Thomas E. McInnes has coded up this DTMF generator object for the Propeller. Written in Spin, the object includes functions for dialing individual digits or a preprogrammed phone number, along with the required Synth object as well as a Demo program. (We note the absence of the “#” and “*” keypad tones in the source code.)
You can download the DTMF object source and demo in a zip file from the Propeller Object Exchange Library. This object has been released under the MIT License.
If ‘#’ and ‘*’ are missing, then I assume ‘A’ ‘B’ ‘C’ and ‘D’ are missing as well.