For 4 people Konftel Ego, Konftel 300IPx and Konftel 300Mx will fit your needs.
For 12 people, the Konftel 300IPx and Konftel 300Mx is a good choice..
At 20-25 people, the Konftel 300IPx and Konftel 300Mx fits with extra microphones as an accessory. For more than 20-25 people, the Konftel 300IPx fits with Konftel PA Interface as an accessory.
Konftel conference telephones
Work environmentally friendly in a global world with personal meetings at a distance using Konftel conference phones.