Cell phones don’t need satelites any more than landline phones.
Actually, the modulation (CDMA) used by Sprint and Verizon, as well as the 3G mode used by AT&T (W-CDMA) do require the use of GPS for precise timekeeping at each cell base station.
Precise time-keeping is used to synchronize the signal from a handset when received by multiple stations simultaneously (it's called a "soft hand-off").