Use Google Voice, then it's free.
Maybe it'll only integrate if you use Google Voice.
I am using Google Voice. It's the international text part that's going to be a huge problem.
Google Voice until now officially still has no support for international texting. What is happening right now if you send an sms to international number, it is up in the air whether your text will get delivered, or if it did, whether the reply will get to you.
I've tested this extensively with my friends from around the world (at least 20 numbers from at least four different countries. The result is, there is no consistency. It's not guaranteed that the sms will be blocked (sometimes it does), but it will also sometimes get delivered. And this happens both ways. It's pretty much about fifty2 chance whether you can actually have an international sms conversation through GV.
This depends not only on the country, but also specific carriers within that country. Different carriers may give you different results.
Now, can you imagine how big of a mess this is if I am in the middle of conversation with someone and then lost data connection intermittently (let's say I'm on the bus/subway) and whenever it does it defaults to SMS? If everything is pure data (like Hangouts is now, and other programs like Whatsapp, etc). Then it's clear that my message wouldn't get through if there's no data, and then it will get delivered as soon as I get data connection again. Simple.
Additionally, GV also doesn't yet officially support MMS, which creates another complexity to the whole thing.