A heck of a lot, and all current phone standards are based on it including current GSM.
GSM used TDMA which sliced a frequency into time slots. The time slots are allocated to the phones whether there is talking or not. This also leads to a fixed number of connections per frequency, and adjacent towers can't use the same frequency. It is also not forwards compatible since the phones expect certain behaviour from other phones in terms of using the time slots. That is why GSM carriers had to go out and get new frequencies when they added 2G data.
CDMA just has all phones broadcast at once. The phones merely see others as noise. When there isn't anything to transmit (voice calls have a lot of silence) then not much is transmitted. The tower will direct power levels to phones to keep the noise as low as possible. The net effect is that there isn't a fixed number of connections per tower/frequency, adjacent towers can use the same frequencies and it is forwards compatible - other phones can use newer versions and it won't affect current phones. CDMA is a lot harder engineering.
Here are a bunch of articles describing it in more detail from someone who worked on it.
GSM used TDMA which sliced a frequency into time slots. The time slots are allocated to the phones whether there is talking or not. This also leads to a fixed number of connections per frequency, and adjacent towers can't use the same frequency. It is also not forwards compatible since the phones expect certain behaviour from other phones in terms of using the time slots. That is why GSM carriers had to go out and get new frequencies when they added 2G data.
CDMA just has all phones broadcast at once. The phones merely see others as noise. When there isn't anything to transmit (voice calls have a lot of silence) then not much is transmitted. The tower will direct power levels to phones to keep the noise as low as possible. The net effect is that there isn't a fixed number of connections per tower/frequency, adjacent towers can use the same frequencies and it is forwards compatible - other phones can use newer versions and it won't affect current phones. CDMA is a lot harder engineering.
Here are a bunch of articles describing it in more detail from someone who worked on it.
http://denbeste.nu/cd_log_entries/2002/10/GSM3G.shtml (politics, tech, how CDMA happened) http://denbeste.nu/cdmafaq/cdmatdma.shtml (tdma versus cdma) http://denbeste.nu/cd_log_entries/2002/04/Howspreadingactual... (what actually gets transmitted)