It's definitely the exact same real 911. You get a real 911 call to the same group of people who would take any 911 call in your area. It's the same. The "e911" part of it doesn't have anything to do with it being VOIP. e911 is a method of having your address automagically sent to the 911 dispatcher.
The issue has never been (except briefly for a couple of months back about 6 years ago) about reaching a real 911 person - it's about getting that person your address instantly.
The thing gets confusing because there was a brief period of time back around 2005/2006 where Vonage had problems linking their system to e911 and they set up their own 911 operators to take calls that were bounced back to them due to the way that they'd messed up setting up their system. But this was a temporary thing about 5-6 years ago and it stopped a long time ago. At the time it got a huge amount of negative media attention - and, in fact, spurred the FCC to much tighter regulation of VOIP providers regarding 911.
The situation Silverpig described has happened in the past but the system is pretty good nowadays and I haven't heard anything bad about it in literally 5+ years. I'm not saying that things are absolutely perfect in all cases - I actually have no way of knowing if they are or not - but I do know that I haven't heard any VOIP 911 disaster stories in the media in a really long time. In the absolute worst case, you might have to tell the 911 dispatch your address, or you might want to confirm it with them.
If you google "vonage 911" or "voip 911" and read the horrible stories, they all date back to 2005/2006. Nothing recently.
Nowadays all of the VOIP 911 complaints are about the fee.
