This is called "group-paging", and will work on most digital and IP phones. The maximum members per group is 32. There are special applications you can enable that will allow you to exceed these numbers.
Special Application Guide:
SA8927
–
Increase Paging Groups
Special Application SA89
27 increases the total number of paging groups to 256 for the small
platforms and 999 for XL. The total members per group will not change.
and
*new* SA9096 Increase Paging Group Members
By implementing this feature customer shall be able to administer paging group members up to
127. The call flow and call processing will remain the same for 127 group
members as it used to
work earlier for 32.
Minimum load - CM 6.0
You can't nest paging groups. I'm not sure why the number 32 was chosen, I've heard speculation it had to do with older phones drawing too much power if you had, say, a whole cabinet trying to page at once. Be careful with special applications -- Avaya doesn't want them on if you run into issues with the system. Also, if this is paging to be used for life safety (evacuations, safety announcements etc) please don't use group paging. There are many situations that will prevent a phone from receiving the page (off hook/in a call/disconnectes/send all calls)