asterisk users - Mar 2005 - how to optimize sip??

I remember reading somewhare that you should disable as many unused codecs
on sip phones as possible to reduce bandwidth.

I'm not sure what I have to do for each type of device I'm using.

I have 2 sipura-2000's and 2 Grandstream BudgeTone 100's and a
sipura-3000, and a few Xlite PC clients.

What do I need to do for each device to reduce the overhead, and disable
codecs that I'm not using.

What codecs should I be using?

Thanks

Pat