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I know teamspeak can use multiple codecs depending on what you set it up as it can use speedex/clep/gsm

http://www.speex.org/comparison/

According to that the speedex codex can use as little as...

-Is your service 3g? If so you should be able to get up to 2mbps
-If you cant get anything faster you would need a service that uses less bandwidth. This of course would compromise the quality of...