The following links provide direct access to the VoIP service provider's Web page regarding their support for 9-1-1 emergency calling services.
AT&T CallVantage
Broadvox
Dialpad
Level (3)
Lingo (Primus/Lingo)
Net2Phone
Packet 8 (8X8)
Speakeasy
SunRocket
Time Warner
USA Datanet
Verizon VoiceWing
VoiceGlo
VoIP.net
Vonage
http://www.vonage.com/features.php?feature=911