This document discusses the progress of SIP (Session Initiation Protocol) in connecting telecommunications networks. It summarizes that while SIP trunking is making progress in replacing older technologies like TDM and ISDN, full integration is still ongoing due to issues like fax support, E.164 number resolution between carriers, and challenges in upgrading the OSS/BSS systems that support billing and provisioning. The document concludes that the real barrier remaining is financial, as carriers struggle with declining revenue as networks transition to IP.