This is a REAL Blue Box Emulator. Instead of an actual Blue Box made out of hardware, you can utilize this completely free web application that will generate the MF tones used by Blue Boxes.
To use this, it is suggested you couple your computer's audio output to your telephone's mouthpiece with little to no space inbetween. You should a headset with earpieces large enough to snugly fit around your telephone's receiver. It is suggested that you use a standard telephone (i.e. Western Electric 500 or 2500) with a G-series handset.
Use either the number keys above the letters or your keyboard's numberpad (make sure NUMLOCK is ON) for digits 0-9. Use K for KP and S for ST. Use H for 2600 Hz.
To use this Blue Box, connect to a switch that allows Blue-Boxing (i.e. a restored SxS system) and utilize 2600 Hz to seize the trunk. Immediately after, MF KP (K), then the area code followed by the telephone number, then ST (S).
To watch a video demonstration, click here. (Note that this web-based Blue Box itself was made after the recording of this video, but everything else should be the same. You could also download and use the WAV files themselves, as was done in the video, but that is more cumbersome. You can download the WAV files by viewing the source code for this webpage.)
No keyboard? Click here.