Out in the woods we can either make use of a Wifi hotspot or stay at a private campground that provides Wifi of some sort. A cell tower needs to be within 5 miles and be within your line of sight. We have gotten reception on top of a hill but not down in the valley where the campgrounds were located. This is where our little Mifi unit and a small laptop are great.
Last year we stayed at a USFS campground at Indian Creek Reservoir and we were able to connect and do email by hiking about 3/4 mile up a trail and gaining some elevation and line of sight for the tower.
For the camper a roof top antenna and an inside amplifier can double the signal strength and this can make all the difference in the world in establishing a connection.
Cell towers are placed along highways to serve motorists. The closer a camping spot is to these highways the better your reception is likely to be.