Voice is a vibration (roughly 60 to 1100 vibrations per second [Hz]) within the audible frequency range. In the human, voice is largely produced by the true vocal cords, but it is possible to vibrate other structures and create a voice.
For instance, there are times when a larynx is completely removed when trying to cure a person of laryngeal cancer.
A person might then use an electronic device to communicate. When held against the neck, the vibrations generated by the device resonate inside the throat creating a voice. However, current devices typically produce a single tone at a single volume. Speech will tend to sound robotic, it lacks the emotion that is present in a normal voice where volume and pitch can be varied.
A person without a larynx may also learn how to swallow air and bring it back out of the stomach. The esophagus (swallowing tube) is soft and flexible enough to vibrate and it is possible to belch fast enough to carry on quite a conversation that is a little less monotonal than with an electrolarynx.