The basic DTMF telephone keypad used in the simulator is a 3×3 matrix of push buttons. I have added an extra row and it contains three buttons or keys : The call emulates 'make a call' key, it generates the 440 Hz dial tone signal, the callbutton terminates the call and the third key textsms is an interesting and a useful feature : it allows the user to send a text message or an SMS anywhere in Canada provided that the user knows the service provider of of the messaged party.
The numeric keys 0 through 9 simulates the electronic signal of the DTMF phone, it combines 2 frequencies or tones for each pressed key. For example pressing key 9 produces the sum of an 852 Hz and 1477 Hz signals.