Comm path has several factor. Height of tower and transmit power. All cellphones adjust their transmit power based on just what is needed by basestation receiver to get a reasonable bit error rate. This is part of the cell site reuse. On GSM, in a urban area, the frequency slot is reuse on basestation four or five cells away. This is how the cell system gets greater call handling capacity. Your phone also reports the basestation signal strength and the basestation will reduce its transmitted power accordingly. Too much transmitted power will just cause interference to other users in farther away cell sites. For CDMA it will degrade other users on same local cell site.
For rural areas where cell site density is lower (farther apart) you have more chance to be farther away from a cell site. This requires your transmit power to be greater which, in turn, consumes more current from battery and reducing you battery life. A GSM phone's transmit power ranges from a few milliwatts to almost 2 watts, with the transmitter final ranging from about 50 mA at low power to about 1800 mA for 2 watts output in 800/900 MHz band. This transmitter current is only for the active transmit slots. CDMA runs up to a watt or about 800 mA for transmitter but it is also on almost continuously during a call.
Cell site density is a factor of economics and statistical call handling capacity needed in a given area. In a dense urban city with a lot of cellphone users there may be a cell site every few blocks. In the country, with low cellphone user density, they may be 10-15 km apart.