CDMA
Knowing exactly how CDMA works is too confusing – even for a geek like me – to explain. However, what it refers to is the way the phones using the technology speak to the base station. Basically, it works like this: You need to think of a wireless telephone system as a crowded nursery school classroom, with lots of small children (the phones) trying to attract the attention of the teacher (the base station).
One way of allowing all the children to speak is to give each one a "turn". That's inefficient, as even the children who don't want to speak are given a turn and if they say nothing then the space allocated to them is wasted.
Of course, with phones those turns consist of microseconds so that there's no audible interruption to the person speaking. That's known as Time Division Multiple Access (TDMA) and was the old way of doing things.
CDMA is currently in vogue and the "teacher" is much smarter and lets all the children talk at the same time. Because she can pick up the different tone of voice of each child she knows exactly what each one is saying.
In the phone world, each phone is given a code that identifies it so the base station knows which unit is speaking to it. Therefore it's limited not by the amount of time slots but by the amount of spectrum available for sending and receiving signals.
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