Before 1xRTT was implemented, CDMA's old 13k bps vocoder sounded
decent.  Now, they use a variable rate codec that sounds really shitty.  
It reminds me of the robot on "Lost in Space":  "Danger Will Robinson!".  
GSM's 13k Effective Full Rate codec is much cleaner.  If you want a CDMA
phone, buy an OLD one.  One that is NOT 1xRTT because it will only support
the 13k codec and the network is backward compatible with the older
phones.  

    Understand, however, that Cingular GSM has implemented a lower bit
variable codec to increase capacity.  I have not heard it yet, but my
suspicion is that even though it will probably be better than the terrible
codec used by CDMA 1xRTT, it will not be as clear and "near landline"  
quality as GSM's 13k EFR.

    Because GSM uses time division multiple access, sometimes the packets
get dropped and you get digital dropouts in the conversation.  CDMA
suffers less from this because CDMA is always in contact with more than
one tower at the same time.  I know some people prefer the crappier voice
quality of CDMA with the benefit that you get fewer dropouts in the
conversation.  Personally, I think CDMA has really shitty voice quality
now that 1xRTT is in place and I think it is appalling that more people
don't complain to their carriers about how shitty their phones sound.

RDT

In correct.  The CDMA receiver is called a rake receiver, it has
several 'channels' with adjustable time delays that can be used to
improve reception by folding all the received signals into one. Those
signals can be from other towers, or strong multipath reflections. If
memory serves me the receiver has 3 or 4 such 'channels' on the mobil
side.

As for implementation, I don't there is much difference. Just plant
the equipment, connect it to the switching center, and turn it on.
Then it gets tweaked for optimal coverage, but I doubt there is a
whole of difference in the effort.

It generally won't pick up multiple towers. There is not multiple
capacity in GSM, adjacent cells use different frequency allocation, so
any channel in use in one cells, may be in use somewhere else, but the
distances on the ground are such that the signal will be far below the
signal for the correct tower, will have incorrect timing, and has very
little effect. As long as the intefering signal is 10-15 db below the
desired signal, it is doubtful that it will have an measurable impact
on the call.

That more a matter of some design issues with CDMA networks. You
minimize energy in the band for maximum capacity, and that means you
try to minimize the bandwidth you use for the Vocoder. The CDMA
Vocoder is delibrately designed to degrade voice quality as network
loads increase, to increase capacity. the GSM Vocoder runs at a fixed
rate, with a pretty good algorithm. The net result is GSM networks
don't degrade gracefully as they overload, they just don't accept new
calls, or handoffs simply fail. SO voice quality is pretty much an all
or nothing situation on GSM.

 I have used Sprint PCS, Verizon Wireless,

Most echo's are the result of issues on the landline side of the
network. It is pretty hard to produce them in the Air link.

"Sort-of" true. When adding cells to an existing network GSM (and all
FDMA and FDMA/TDMA) technologies needs frequency planning to avoid
interference. In a worst-cas scenario other cells needs to be
re-planned not to interfere with the new one.

In CDMA all cells are on the same frequency, so no frequency planning.
Great, BUT, instead You need power planning. Too much transmitters on
CDMA and You will increase the noise floor. Power is everything, and
power planning in CDMA can be much harder than frequency planning in
CDMA.

Also "sort-of" true. The principles are fundamentally different. To a
CDMA receiver, the same signal from different sources is used to
improve the receive quality,but all other transmitters are considered
noise, so yes, too many towers reduce capacity as they increase the
noise floor. In GSM, all towers (in each area) are on different
frequencies and the phone holds a database of available towers and on
which channel to contact them. When roaming to the next one, handsets
change frequency unnoticeable to the user.

Only the basic principle is the same, not the implementation.

BS. WCDMA is more fully speced than any of the CDMA2000 versions which
are hampered by the 1,25 MHz bandwidth to be compatible with CDMA-One.

WCDMA sounds pretty good though...!

/Marcus