POMPs stands for Peace of Mind Packages
As far as Maint yes after 1 year on PBXact you pay a yearly POMPs to get updates to the system as a whole. With FreePXB you dont pay for upgrades but if you use Commercial Modules you have to pay a yearly maintenance to upgrade those commercial modules of 18% of the module price if over 100 and 30% if under 100.00.