Full-duplex vs. half-duplex - Both walkie-talkies and CB radios are half-duplex devices. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time. A cell phone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. Both people on the call can talk at once.
Channels - A walkie-talkie typically has one channel, and a CB radio has 40 channels. A typical cell phone can communicate on 1,664 channels or more.
Range - A walkie-talkie can transmit about 1 mile (1.6 kilometers) using a 0.25-watt transmitter. A CB radio, because it has much higher power, can transmit about 5 miles (8 kilometers) using a 5-watt transmitter. Cell phones operate within cells, and they can switch cells as they move around. Cells give mobile phones incredible range. Someone using a cell phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach.
In a typical analog cell phone system in the United States, the cell phone carrier receives about 800 frequencies to use across the city. The carrier chops up the city into cells. Each cell is typically sized at about 10 square miles (26 square kilometers). Cells are normally thought of as hexagons on a big hexagonal grid, like this: