Some customers have had the suggestion that when a CS client for example, can't log into their CS server, have the client let you know that port 443 or 35060 is currently being blocked or similar.
You can always run a tool like Zenmap - Official cross-platform Nmap Security Scanner GUI
You can do a basic scan on ports that will in most instances tell you whats open or not (TCP only)
A scan expression like this will scan common Lifesize ports.
nmap -sS -p T:80,443,1720,5060,8181,35060 <ServerIPAddr>
Retrieving data ...