asterisk users - Apr 2006 - record_in / record_out configuration parameters

Hi all,
having performance problems with various SIP-Phones, the manufacturer 
adviced us to add these parameters in sip.conf - unfortunately, neither 
one of us has an idea what these are supposed to do.
I've seen various configuration files (sip.conf, iax.conf) posted on the 
net or this list using said paramters, but they seem to completely lack 
documentation (or is it just me?).
Grepping for them in the asterisk sources (and those of related 
packages) didn't show up anything either. We're running asterisk 1.2, 
just in case they're old parameters which have been removed or more 
recently added ones...
Could someone in the know give a short explanation of what these 
actually do?

Thanx in advance,

Flo