This should be a new chapter of a much shorter depth than the previous version. We may work a glossary-like version that explains common terms (20-30) and compares them in various solutions and points to the appropriate term native to each. Include references to outside material for a more detailed analysis.

General Terms

VoIP protocols

H.323 and SIP

VoIP codecs

G.xxx

VoIP services

general
value-added
enhanced communication services

SIP Proxy server

H.323 Gatekeeper

Agent - client - endpoint

Gateway

Media proxy

PBX

Call routing

NAT traversal

SIP-related Terms

Domain

Identity

TLS

SIP.edu

ITAD/ISN

Telephony Terms

E.164

Definition.
link for National prefixes

ENUM

Golden-tree and unofficial ENUM trees
Differences between infrastructure ENUM