Cells phones - because they're always trying to cell you the latest model.........

Or is it that the transmitting masts are arrayed in the best places to cover the whole country (alledged) and phones only communicate via the one transmitter. The area (volume in truth) covered by any one transmitter can vary with weather and buildings, cranes, aeroplanes, dirigibles etc. However for the purposes of locking onto phones and handover to the next transmitter when you are moving the sphere of capture is called a .........

sorry - out of range (no cell)