Wireless communications between cell phones and towers take place at a range of different frequencies. In general, transmissions at low-frequencies tend to be well-suited for offering extensive coverage. Low-frequency transmissions aren’t particularly well-suited for transmitting large amounts of data. Transmissions at high frequencies typically can’t travel long distances as well as transmissions at low frequencies. On the flipside, high-frequency transmissions tend to be better suited for high data throughput.
The government regulates who is allowed to transmit signals at certain frequencies in the electromagnetic spectrum. Cellular companies can purchase transmission rights in the FCC’s spectrum auctions. Spectrum is a major expense for network operators. The largest spectrum auction in U.S. history recently closed with several billion dollars spent by cellular networks.
A phone must have compatible hardware to communicate at a particular frequency. A detailed description of a phone’s hardware will usually include a description of which technologies it supports at which frequencies. For example, a phone’s specifications list might include:
- LTE bands 2, 4, 12, 13, 25, and 41
- CDMA at 850 and 1900 Mhz
A “band” indicates a range of frequencies that a phone is compatible with. E.g., band 2 includes transmissions between 1850 and 1990 Mhz.
Some bands are used by multiple networks (e.g., several U.S. networks use band 2). Other bands are used by just one network (e.g., T-Mobile is the only major network using band 71).
A phone sold by a wireless carrier will usually support most of the bands the carrier uses. However, phones sold by a given carrier won’t necessarily support most of the bands used by other carriers.
Phones that are compatible with only some of a network’s bands might be able to connect to that network. However, performance may be lousy if important bands are missing. PhoneArea has an excellent article covering the frequency bands used by each major U.S. network.