This looks interesting. Do you need any pbx or if i got 5 IP phones, set them up, they would just work? Need to crunch some numbers on per minute vs flat rate

This looks interesting. Do you need any pbx or if i got 5 IP phones, set them up, they would just work? Need to crunch some numbers on per minute vs flat rate. One of the businesses is phone intensive, probably use 120-240 minutes per day.