Let me assure you that it does. However, it's not exactly in any of the maze of acronyms and protocols used by VoIP. E911 is a service provided by the VoIP service provider. I'm currently on two VoIP services and I don't know how many private Asterisk switches. The service providers all offer E911 service. The gateways generally do not. That's because the VoIP service providers are required by the FCC to provide E911 service if they are connected to the PSTN (public switched telephone network): "The FCC requires that providers of interconnected VoIP telephone services using the Public Switched Telephone Network (PSTN) meet Enhanced 911 (E911) obligations. E911 systems automatically provide to emergency service personnel a 911 caller's call back number and, in most cases, location information."
E911 service is often not provided directly by the VoIP provider. Instead, an E911 gateway provider supplies the direct connection, and charges the smaller VoIP service provider some charge per line, typically about $0.80/line/month. The VoIP provider passes on the cost to the customer, typically at about $1.00/line/month. For example: VOIP 911 Service Providers
Coming real soon now will be NG911 (next generation 911), which among other things, will allow submitting emergency "calls" via VoiP, SIP, WebRTC, email, SMS text messaging, chat programs, handicap comm devices, smartphone video, images, carrier pigeon, and smoke signals. I'm told this will all be a good thing. (3:13)
At this time, there are a maze of geolocation schemes designed to provide location information for VoIP phones. Mostly, they involve either programming the users location into the instrument, or using a GPS inside the phone. Geolocation protocols are still being hashed out. Note that for NG911, altitude and building floor number are of importance. If you're the fire department, and you arrive at a structure fire in a multistory building, it's important to know the floor number.
Here's an old example of one way to do it using DHCP: "Dynamic Host Configuration Protocol Option for Coordinate-based Location Configuration Information" It's not going to be used, but does give a clue as to how it might work.