Echelon doesn't monitor voice, it monitors data.
It monitors both:
Echelon is perhaps the most powerful intelligence gathering organization in the world. Several credible reports suggest that this global electronic communications surveillance system presents an extreme threat to the privacy of people all over the world. According to these reports, ECHELON attempts to capture staggering volumes of satellite, microwave, cellular and fiber-optic traffic, including communications to and from North America. This vast quantity of voice and data communications are then processed through sophisticated filtering technologies.