Hangouts is Googles iMessage
And I quite like the way they separate it. Before you type your message the input box has a greyed out message on it; either Send SMS to [phone number] or Send Hangouts message. you can change this by pressing on the icon in front of the message. Better yet. If the user on the other end of the conversation doesn't use hangouts. you can only send a text. It works. Plus it becomes your hub for video chat and VOIP too, though I haven't played with voice calls yet when my phone does a perfectly good job of that already.
What I do't understand, and this is cross platform, why is there so much buzz about the ability to save your text messages when you switch devices? Or even make text messages an important part of a backup. This goes for iPhone and android users.
If there is any important information sent to me via text then I wouldn't really like to keep it in such a fragile ecosystem. If you need the info then simply copy paste it, put it in notes, email it, dropbox, google drive. lots of other places but not you SMS inbox?!
I suppose there is always the sentimental factor. Maybe it's because my wife and I no longer send soppy text messages to each other that I have become jaded to the whole thing.