Cellular Phone System:
- Each cell has a base station with a tower which receives and transmits signals.
- All the base stations are connected by phone lines to mobile telephone switching office (MTSO).

How does it work?
A caller communicates via radio channel to its base station, which sends the signal to MTSO.
If the called number is land based, MTSO sends the signal through central telephone office like any other phone call.
If the called number is mobile, MTSO sends the signal to the base station of the cell where the called number is. The base station transmits the signal to the called number using the available radio channel.
As the caller moves from one cell to another, MTSO automatically switches the user to an available channel in the new cell.