Wow, great question. DTM and F are what we tech people call “letters.” Letters can be strung together to form words. Now, DTMF is an advanced string which we call an acronym. (Before you ask, an acronym is a word formed by the initial letters of a phrase)

Are you as bored as me? Must be if you’re still reading this… but anyway we digress…

The acronym DTMF comes from the phrase Dual-Tone Multi Frequency. Basically, if you have a “touch-tone” phone (at Voip Tech Chat we get paid every time that we use quotes) you can hear a special tone when you press a number. If you’re a really bored person, you can even use these tones to make music. For example, if you wanted to play Mary had a Little Lamb, you can press:

3 2 1 2 3 3 3 2 2 2 3 3 3 3 2 1 2 3 3 3 2 2 3 2 1

Now, before you do this, make sure you aren’t using a phone having a dial tone, or you’re gonna make a call that may cost you some money.

Anyway…

The short story here is that when you press a number on your touch-tone telephone, a frequency is sent over the line. At the other end of the line, the system can then interpret these frequencies and determine the number you dialed. This is useful for, let’s say… dialing a phone number. It can also be used to make selections in automated phone systems, etc.