Giovanni Carrera blogged about his touch numeric keyboard for Arduino or Teensy:
Very often, for our programs, we need a system to set parameters, usually of a numerical type. A 4×4 keyboard requires some space and then we also need a display. Here is the idea of using a touchscreen display to do both. I have then written the GetNum function that allows you to print a prompt message and to type an integer number. To test this function I wrote a simple analog data logger program that required two parameters, the first is the sampling period and the second the number of samples. In this example the number of channels to be scanned is set to three, but the program can be modified to request a third parameter with the number of channels.
See the full post on ArduPicLab blog.