I have been using Voice since like 2007, it's one of the only services from Google I've latched onto because it's nearly impossible to steal a phone number out of it (nobody to social engineer and need to get access to Google Account and pay a few dollars to unlock the number). For YEARS, like 5+ nobody knew if they were shutting it down. It used to be possible to trunk SIP calls over Google Voice using GChat/Gtalk and XMPP to SIP bridge.

Out of nowhere they started to update it again sometime in the latter part of last decade, it still has 2 panels in the configuration backend because they halfassed implementing the Material interface and didn't include all the features. Despite this I'm ride or die with it because there's nothing else on the market that gives you a fairly un-stealable number for free.

Oh and to continue the fragmentation, Google Voice for Workspace is a totally different product similar to Vonage Cloud. As has often been the case with their paid services for years, the free users generally get a better experience.

EDIT: I honestly think a big part of the reason this has stayed running is Bandwidth.com runs most of the show under the hood and that company knows what they're doing. Another Google service they ran was GOOG-411 when that existed.