The Alternative

In an online document written by Tektronix, Inc. explaining how CDMA is the alternative for the lacking GSM networks.  

CDMA technology took a large share of the market. Because spread spectrum uses wide band, noise-like signals, they are hard to detect. They are also difficult to intercept or demodulate. Further, spread spectrum signals are harder to jam (interfere with) than narrowband signals. These Low Probability of Intercept (LPI) and anti-jam (AJ) features are why the military has used spread spectrum for so many years. 

CDMA towers have hundreds call and data receivers on their structures, versus GSM towers that only have a few receivers on their structures.  CDMA sites can take in almost as much as 10 calls per second for every call receiver. It then authenticates the origin of the call which is then sent to the switch for the call destination.  Their towers are also more efficient by using a different standard then GSM.  CDMA towers have completely seperate data receivers and voice receivers all on of their towers.  This allows voice dedication for all calls and seperate data dedication.  The importance of this is simple.  On a CDMA network data, is always running around 900 kilobites per second (vs. GSM running at around 500). If data and voice were to be running through these sites at the same time, all voice calls would be cut off, because, like we explained before, data always has priority.