Hi Leonard! :-)

 LE> *Any* cell phone network "allows sharing" or it wouldn't work. But 
 LE> each phone needs channel to the chell tower. And there are only so
 LE> many channels *possible* in a given band.
Yes, and then you can also use time domain multiplexing to share time slots
on one channel between multiple phones. Plus the channel is only used when
a conversation is taking place. Control messages go on a seperate channel
used by all phones, using a collision detection scheme for access control.

This means more phones can be registered with the network in a cell than
can actually be used for phone calls at the same time. The assumption is
that not everybody wants to talk at the same time.

 LE> Doesn't change the problem I was talking about. Namely, that for any
 LE> "type" of network, there is a *small*, *finite* number of channels
 LE> available. 
True. I don't think any technology can change the fact that only a finite
number of people in some area can use their mobile phones at the same time.

 LE> So as the number of phones *simultaneously* in use in an area goes 
 LE> up, you have to go to smaller "service areas" for each
cell tower so as 
 LE> to have enough channels available for the traffic. 
I think what the GSM providers here do is use overlapping service areas.
Since the same frequencies are only reused two cells away, you can have
adjacent cells overlap halfway. This doubles the number of channels
available to a phone operating in the area, since it can be handed over to
the other cell if one of them is full. This doesn't really give more
channels, but makes load balancing between cells possible.

 LE> *Or* you have to have more than one "type" (frequency band or
 LE> modulation) of cellular service hosted at the sites, with (hopefully) 
 LE> a decent mix of phones able to use one or the other or both.
That's not very different from just allocating more frequencies for one
type of service. Plus there's no good way to guarantee that people will
have different types of phones -- you can still end up in a situation where
everybody contents for one type of cell service.

Ciao
Pascal

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