Web browser plug-ins such as Flash already provide VoIP functionality in a web browser, but is it possible to have browser VoIP without any plug-ins?
Ericsson Labs has posted information using the device element to allow for microphone input. This, in addition with WebSockets could be used to implement VoIP. However, the device element is not implemented in any web browser yet.
No there isn't but the device element will likely be the way in the future, as you mentioned. I don't think it will take too long for browsers to look into it however. There are also the WAC APIs, but they are only on mobile, and not shipping quite yet.
Update: There is now a standard in development called WebRTC. Drafts of this spec are supported by Chrome and Firefox. Microsoft have made an alternative proposal called CU-RTC-Web
