press the DND button on your phone

Yes, but the customer do not want to use DND button on the phone, but *78 and *79

I prefer to use button instead on feature codes, but in this case i do not have the choice.

When i use linksys phone, *78 activate DND function on the phone. Is it possible to do the same thing with aastra phones ?

Linksys software programs VSC(vertical service codes) into their phones. Even though you dialed *78, its simply pressing the DND button making the phone return a BUSY sip message on an INVITE. So technically, dialing *78 is a crude 3-button approach to just pressing 1 button :).

As far as doing it in the system you could do it this way:

1. setup a feature code to go to voicemail. We prepend 7 to the extension so if your extensions are in the 100s range then the pattern is _71XX with 1 digit getting stripped. Calling 7101 sends it to the voicemail box of 101.

2. Forward your phone to 7+your extension, you could even make a feature code for *78 that does just that. Then *79 would just become a remove forwading script.

obviously this would not stack with forwarding since it _is_ forwarding. Whereas DND from the phone has no impact on forwarding at the PBX level, as it never calls the phone to get a BUSY.