This is an issue I've been tracking, namely how well do the VOIP providers provide emergency dialing service. The VOIP providers want to replace the normal telephone companies, so the VOIP providers had better be able to provide all those services. But as I've noted in previous postings, some of the VOIP providers are dragging their feet.
Look at this report from a Vonage user: could not dial an emergeny # on vonage tonight The summary is a small child had swallowed something, and they needed to reach a poison control center immediately, and couldn't get through on their Vonage line. After a couple tries to dial on Vonage they switched to their cell phone and went right through. In the followups as others gave their own horror stories.
Another forum posting, Tips for doing an E911 Test Call discusses testing your E911 service. You have to make it clear with the emergency desk that you're running a test, and in some areas it's illegal to make a 911 call except for a real emergency. I wonder how individuals are to be assured their E911 service works unless they run a test?