asterisk users - Feb 2004 - CallWaiting CallerID: Available on all channel types?

I have some phones that purport to handle this properly but am having 
quite a time figuring out just when to expect it to work and when not 
to.  Limited to Zap channels?  Zap and SIP, but in different manners?

Sieving the list archives yielded more questions than answers.

Pointers or discussion appreciated.

Thx.

B.