Have you ever wondered what is radio spectrum?
The electromagnetic spectrum can be broadly classified into 7 types of which radio spectrum is one. radio waves have frequencies ranging from 3kHz to 300 GHz.
Radio waves are of 4 types: Medium frequency (used for radio), High frequency(short broadcasts), Very high frequency(TV) and ultra high frequency waves (used for mobile and wireless transmission). In the USA these spectra are allocated through auctions and have so far generated about $60 billion.
The ultra high frequency waves used in mobile phones are in the frequency of 850 - 1900 MHz. A properly constructed tin foil can block radio waves very effectively.