Ah, that's a good suggestion: 'is someone paying Google for this?' This subsumes the advertising covariate I was musing about (I didn't bring it up because looking at a bunch of the dead services, I didn't know how I could possibly check whether advertising was involved). I'll add that.

And yes, I would be worried about Voice's long-term prospects, but my impression is that it won't be going away within the next 5 years, say. They've sunsetted the Blackberry app, and neglected the service, but that still leaves the main service and 3 other apps/services according to my current list.