Another technology that uses waves are cell phones.
Unlike GPS, which uses radio signals, cell phones use digital code. When you speak into a cell phone, your phone converts the sound of your voice into digital code before transmitting it as a radio signal.
The radio signal is picked up by the nearest cell phone tower in your network, and these towers are located in various cells (hence, the name cell phone). The tower redirects the signal through the network to whoever you're speaking to. His/her phone must convert the digital information back into the sound of your voice.
For more reading on how a cell phone works, check out How Stuff Works article on just this topic!