Hi Peter, I'm afraid you misunderstood me - I would *love* the BLF on my Yealinks to indicate the DND status of the extension presence - I was indicating the attitude you'll find from other 3cx users.
I have raised this several times - coming from the Asterisk world where dialling the DND code on an extension is indicated on monitoring BLFs as busy
I'm afraid this is just going to have to be one of those things you live with

since I don't believe you'll get enough votes in the ideas section to have 3cx look at changing how it currently works.
I am still totally torn. I love the "unified client" concept of 3cx although the chat system really is quite abysmal and needs work. Right now, the nearest competitors are well-known... one of them provides a mobile client but the desktop client looks overly fussy. The other has a mobile client in beta and right now doesn't hold a candle to 3cx. Yet, some of the "eccentricities" of 3cx make me quietly fume as it could be SO much better. Things like 1) why do I have to use the overly-restrictive call queue module if I want music on early media rather than ringing, 2) why does the SIP forking behaviour differ between a ring group, call queue and directly calling an extension, 3) why does a call queue need to poll for free agents every 1 or 2 seconds - if this was configurable the call queue feature would become 10 times more useful to some (like me).
In short, the BLF is NOT updated and as far as I can see, never will be. The response will, I believe, be "use the web client or windows client to see presence". Totally impractical in many business.
[Edit] Peter, BTW, I should mention that somewhere on the forum someone said they had implemented some kind of workaround which caused a phone to park a call "forever" when in DND so it appeared "in-use" to other phones BLF but I doubt this would be any use in a commercial environment - I don't think the poster was overly-enamoured with his solution either.