Take a SIP
'such as those for IP telephony, will not operate because private IP addresses are not routable over the public internet, and therefore a node outside the network cannot initiate contact.'
I wouldn't want any random spam phone call system phoning users ip phones without some kind of control.
That is why you have a PBX and SIP trunks and / or PSTN or BRI gateway. It's not difficult.
Biting the hand that feeds IT
