of frequencies, it uses many small towers covering areas called
cells. Because the range between the user and the nearest cell is
just a few miles at most, much lower power can be used, allowing
multiple users to employ the same frequency without interfering
with one another. The cells in each city for each provider’s system
are coordinated by a Mobile Telephone Switching Office (MTSO).
The MTSO also handles the connections between cell users and
the regular landline phone system. (This is why a person can use
a cell phone to call a landline.)
Each cell phone has a unique identifying code that it broad-
casts. As the user moves from one cell to another (perhaps in a
car), the MTSO keeps track of which cell the phone is in. If the
phone gets out of range of its current cell, it is switched over to the
An early mobile car phone, demonstrated in 1946, comes with a dial on the car’s
dashboard for making calls. Because they were expensive, few people during this time
period owned mobile phones.
