As you note, it can be fairly simple at minimal cost. Commentors in the IP CALEA proceeding estimated 1 cent per subscriber per month for large subscribers - which seems borne out in practice. The ETSI website contains both the requirements and the specifications that are used in most countries of the world outside the U.S. Go to http://portal.etsi.org/Portal_Common/home.asp and click on "LI." You will find all the specifications. For Internet access providers, the most relevent new standard is TS 102234. In the U.S., go to the www.askcalea.org website and you'll find guidance to all the relevant requirements and standards.