E-911 works with Vonage, at least here in Rhode Island. It may vary depending upon where you live, but make no mistake it is not a technical issue. Instead it is a political issue, political being corporate politics. NyNex at the time was explicitly cut OUT of the E-911 pie, their only role was to provide the trunking and the database lookup. The E-911 system itself belongs to the State of Rhode Island and Providence Plantations. We phone subscribes pay for this system to the tune of a little less than $2 a month.
What this ultimately means is that CLEC's can tap into the same E-911 system without interference from what is now Verizon, and let me tell you that Verizon will drag its feet when it very well wants to do so.