It has been a while back, I did work for a phone IC maker. Now there are new frequencies for cell traffic, that came from old TV channels. (US) Back before that: The CDMA network operates in the frequency spectrum of CDMA 850 MHz and 1900 MHz while the GSM network operates in the frequency spectrum of GSM 850 MHz and 1900 MHz.
I never worked with cell RF but I did work cell audio.
TDMA provides multiuser access by chopping up the channel into different time slices and FDMA provides multiuser access by separating the used frequencies. TDMA is like having 128 phones connected to a 128 position switch that is spinning very fast. Each phone gets a time slot. FDMA each phone has a different frequency with in a carrier.
The CDMA is based on spread spectrum technology. It allows each user to transmit over the entire frequency spectrum all the time.
GSM operates on the wedge spectrum called a carrier. This carrier is divided into a number of time slots and each user is assigned a different time slot. GSM uses both Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA).
I find this complicated, in part because, I come from broadcast where we talk frequency not time. I transmit on 98.6mhz. The RF cell engineers I know talk in time not frequency. If you think time, cell is easier to understand. I am the wrong person to explain this because I have a hard understand "37.5nS later we transmit this then 37.5nS we to that". It hearts my head to think in time.