does vtec work when cold

i dont mean to sound stupid but this is an honest question.

does the engine have to be at a cetraint temp. to kick into vtec.
i have noticed in my d16y8 that it doesnt make any diffrent sound like it does when it is cold at higher RPM's (yes you can hear it when warm, and yes i know it is slow).
i have also noticed the same in my friends 94 vtec (h22) lude.
does it have to do with oil presure?

It's true. Something about the ECU being in warm up mode when you first start it, and not letting you get into vtec to protect the engine against wear or something like that. It's been a long time since I read something about it, I can't remember the full details.

at least i know i am not crazy anymore. i cant find anything about it
.

http://www.honda-tech.com/zerothread?id=366071
From what these people are saying, it does have to do with oil pressure (warming it up will increase oil pressure). I know I've seen more info before, but I can't seem to find anything else.