At one point I had my Google Voice number tied to Hangouts, so SMS came through that app, and maybe one or two friends that also used Hangouts. I was never sure what client or integration they used, because it always seemed disjointed, like the app was made for someone else and I was an edge case so many of the features didn't make sense or didn't work, but I assume they did for someone. The most confusing part was the contacts tab, which had recommended contacts at the top instead of alphabetic ordering. It never made sense. It had about 50% numbers with no name associated. I assume just phone numbers of businesses I dialed at some point. The rest were a mixture of people I've emailed before but never called, someone I messaged frequently, and a bunch of people I haven't communicated with in any way since before Hangouts was even a thing, which I can't fathom why a recommender would decide I might want to call them now.