Don’t choose the office IP phone system by user count alone. A team of 50 might have only a few calls going at once, or a busy support desk with many. The IP PBX models here have different limits for users and live calls, and their prices are shown on the page. If your team is growing, look at what the particular model can handle and whether it has an expansion option. You’ll also see the HA100 here; it’s a backup controller for a compatible PBX, not the PBX itself.