Seriously speaking (pun not intended), can there really be enough energy generated through speech alone? Theoretically, the answer would be yes, but it isn’t too practical to shout into your handset for that to happen – firstly, you will come across as a nut case, and secondly, it will take a whole lot of shouting at length to gather a little bit of juice, by which that time, you might just shout yourself coarse that you can’t talk over the phone anymore. Ironic, isn’t it?
The prototype required nearly 100 decibels, which is roughly the equivalent of noisy traffic or a jet passing overhead, all for 50 millivolts of electricity. Best to bring such a phone (if it materializes, that is) to the loudest night spot you can find, and leave it on the speaker. Now that’s bound to give the phone a literal jump start!