Guess it depends on your comfort level. Like NY Biker said, if you lose electricity, you'll lose the ability to charge a cell phone. In emergencies - large geographic ones - cell towers go down, get clogged, and otherwise become disfunctional. Happens along the Gulf coast during hurricanes.

If you're going to keep a land line, make sure you have an old-fashioned hard wire phone (such as a princess phone) - during a power outtage portable phones don't work.