If it were me, I would set up a calling group that contains all of the extensions that you would like to answer the calls. It is pretty easy if you have the documentation. If you use DID, you can make the calling group match the extensions of your DID group, so when people dial that number it hits the group. If not, you would make it an additional option on your automated attendant, and then point that option to a group. If you don't know what groups you have available, the simplest way is to go to system renumber/single/calling group and then do an "inspect". If you are not doing anything like this today, chances are the only group you have is your voice mail, which is generally 770.
If you are at all familiar with adding extensions to the voice mail calling group, the programming is very similar. The exception being you have to decide whether the group is login or logout (meaning when the light on my phone is green am I an or out of the group.) This way gives you by FAR the most control - service observing, etc.
The programming requires patience and trial and error, but isn't really that complex. I recommend you go to Avaya.com and download the feature/reference manual for the Magix, and read the overview of group calling.
Hopefully this helps - I know there isn't much specific programming in this email, but if you are interested I (or several other people on this site) can step you through it - I am an Avaya Bus partner and Magix tech and there are a heck of a lot of people on this site who know way more than I do, as well
