Crumple a piece of paper up in front of the telephone as you speak into it to make your voice sound crackly to the person on the other end. Continue to crumple the paper while speaking for the duration of your call.
Consume foods and drinks known to increase mucus production, such as dairy products, sugary beverages, fried foods or eggs. Avoid clearing your throat to allow the mucus to build up. When you speak, the buildup will cause a crackly sound in your voice.
Concentrate on speaking lower than your normal vocal tones. Focus on deep breathing. Push air up through your vocal cords, exhale as you speak, and make a conscientious effort to obtain a crackling sound in your voice.
Wear out your voice by spending long periods of time talking or singing loudly. When you speak with tired vocal cords your voice will come out sounding raspy and crackly.
Record your voice and alter the clip in a computer program or synthesizer to change the sound of the recording.