You also have to look at the RTP port range of the devices.
Here are general ports used:
RTP stream 16384-32767 (UDP)
For SIP:
either UDP or TCP 5060 for the signaling
A user agent MAY register with a local server on startup by sending a REGISTER request to the well-known “all SIP servers” multicast address “sip.mcast.net” (224.0.1.75).
For H323
Unicast GK Discovery 1718 UDP
Multicast GK discovery (UDP) 224.0.1.41
Registration/Status 1719 UDP
H.225.0 (call signaling for hosts) 1720 TCP
h245 is negotiated in the range of 11000 – 65535
For MGCP:
MGCP version 0.1
MG and CA signalling – 2427 (UDP)
MGCP version 1.0
MG – 2427 (UDP)
CA – 2727 (UDP)