A bunch of bloggers picked up on Todd's discovery. Dan York, writes "Wouldn't it be great if you could call a Google Voice number directly via SIP? So that you could bypass the PSTN when calling a GV number and go directly over IP? With potentially all the advanced capabilities that could give? (wideband audio, video, etc.) It turns out that you now can!" Dan also discovers that it appears Google Voice is leveraging YATE (Yet Another Telephony Engine), which has been sort of an "also ran" when compared to Asterisk, but is pretty popular in Eastern Europe.
The one beauty of YATE is its support for XMPP and Jingle for IM support, which Google is also a fan of. Google Talk (separate from Google Voice) is based off of XMPP & Jingle. Nerd Vittles also picks up on this news and explains how to setup E.164 and ENUM to work with your Google Voice phone number and your Asterisk-based IP-PBX so you can get free calling from your Asterisk-based IP-PBX to any Google Voice number.
So the killing of Gizmo5 certainly seemed to indicate Google might be itching to support SIP connectivity directly within Google Voice. This would be a killer feature, especially when you consider the free U.S./Canada calling offered by Google Voice. Imagine hooking up your IP-PBX to Google Voice via SIP. You could kiss SIP trunking by smaller providers goodbye. This could also be a preemptive strike against Skype which offers the SIP-based Skype Connect. Imagine the timing if Google announced FREE SIP trunking just before Skype's pending IPO? Although Skype Connect is not Skype's main revenue source, it is one of their fastest growing segments, so this could be a Skype IPO killer!
Another huge potential is that Android devices could have a SIP client that lets you make/receive calls over an IP connection (WiFi or 3G). The 3G connectivity is especially useful if you live in area with spotty coverage. My house has 0 signal bars for AT&T and Verizon.
But hold the phone! Now it appears Google may have pulled the plug on supporting SIP. Look at Todd's latest update:
[Update March 8: It seems this service is no longer working, starting yesterday evening. sigh. I was hoping to see the security bugs patched up, not for the service to be pulled down again like it was in early 2009. Please, Google Voice people, throw us a bone here and let us know what's really going on for once!]
Perhaps they let the cat out of the bag too soon? They want to 'strike' the iron while it's hot - just before the Skype IPO? I wonder...
Also check out the related article from Rich Tehrani on Skype pre-IPO scorecard.