ventrilo (unsure of teamspeak) bandwidth relys on what codec is used. the higher the codec the more bandwidth used. this is why "fly by night" vent resellers sell dirt cheap because you sound like your underwater while being taped by a monkey from behind.
Quoted direct from ventrilo.com- http://www.ventrilo.com/setup.php
Bandwidth usage will be determined by what codec the server instructs the client program to use. The default configuration for a server is to use the GSM 6.10 codec and sampling at 11Khz. After compression this will consume approximately 3K bytes per second per voice stream.
Using the 3K bytes/sec example this will translate into the following numbers. If you are in a channel (not to be confused with a server) and there are 3 other people in the same channel as you:
One of the other people talking will produce 3K bytes of inbound data.
Two people in the same channel talking will produce 6K bytes of inbound data.
Three people in the same channel talking will produce 9K bytes of inbound data.
And so on....
As you can see the mathematics are very simple.
The outbound traffic coming from you and going to the server will remain constant when ever you are broadcasting. Using the default codec you will produce approximately 3K bytes/sec of outbound data.
If the server administrator chooses a different codec and sample rate then the bandwidth utilization will change as well. It might be higher or lower but only the server admin can control this.
Im in no way promoting this next link!
on this providers website it has a screenshot of some of the codecs and there rates, again in not recommending them, i have never used them before and only stumbled across it to show you the codec screenshot!
I know your looking for specific numbers but without knowing the varables noone can give you the "set in stone" answer your looking for, however using the above info and after figuring out the codec your going to use or what ones to offer you can calculate each slots useage. hope this helps