Google Messenger => Android Messages; also see Google wants businesses to text with its Android Messages service (Recode) and Android Messages will be the new default texting app Google wants you to use (The Verge)
"Google sees it differently. For the company with seemingly thousands of messaging platforms, each one with different features and different audiences, RCS presents an opportunity. It could help Android compete with WhatsApp and Facebook, as well as with Apple’s iMessage. iMessage is so appealing because it’s so simple: you just send a message, the same way and in the same app for everyone. It either sends with stickers and balloons to another iPhone user, or gracefully reverts to a simple text message for everyone else. The only difference is the bubble color. iMessage is one of the best (and hardest to leave) features of iOS, a reason lots of people pick iPhone in the first place. Google can’t simply build the same thing and force its success: if it goes to carriers and demand they use Allo, they’ll just say no. Since manufacturers can customize Android to their liking, Google has too woo them one by one as well.Google's Adoption of RCS Will Save Messaging on Android | WIRED
Fortunately, Android’s marketshare is so large, particularly in developing countries, that anything supported across all Android devices would effectively be universal. If Google can convince everyone to play along, RCS offers all the new-fangled features users want, with a fallback to SMS for those who can’t use it. It could be effortless and foolproof. Just like iMessage. Just like texting."