Base stations are spaced roughly 10 miles apart, with variation depending on population, and geographic features.
Line of sight is required between the base station and handset.
There are many part of the country where there are few, if any base stations and other parts of the country where the terrain may affect the line of sight required to receive a signal. Answering services are often provided by the network for when the phone is switched off or out of range. The cost of the handset is often subsidised by expensive calls and monthly rental costs with a minimum contract. A mobile phone can be used to alert the emergency services from a campsite or scout hut which has no fixed phone. It also allows parents to contact you at camp.