Cisco also has a Cisco Qualified Specialist credential for IP telephony that's probably worth looking into. Also, if you visit http://www.gocertify.com and search on "IP telephony" you will find coverage of the Cisco program, as well as programs from Clarent and Avaya. Given that you've already started down the Cisco trail, that may remain your best bet. It's certain that IP telephony is a good subject matter, and should aid your employability for some time to come.
This was first published in August 2002