We have an IP500 ver 4.0.10 with one digital 8 module(6 - 5410 sets) and two analog modules for a total of 16 portable sets. This setup is running the Engenius Durafon Pro's for a rural campus environment with four base units - dedicated extn's. We are constantly having trouble with the portables accessing a line and needing to reset the Engenius base units. Any know issues with this many analog phones on the IP 500. We have used the Engenius units with the Magix and Partner without any problems.