Help understanding the integration between Google Voice, Hangouts, and Messenger I've had Google voice with Sprint since day 1, I love everything about it. Hangouts added some great features like MMS but to search the body of old messages I still have to use Google Voice. 

This makes me believe that Google Voice is the parent service for my Google number/Sprint integration and Hangouts is just an app that intercepts new messages and updates Google Voice records. 

Now there's Google Messenger. When I launched the app today I saw some but not all of my Hangouts messages and when sending a text, new messages were not updated in Voice or Hangouts. 


Why did only some old messages show up in Google Messenger?
Why didn't new messages sent from Messenger show up in Voice/Hangouts?
It's important for me to keep all my old voicemail/MMS/texts as well as logging new ones so, should I not use Messenger and instead keep using Hangouts?
If Messenger isn't integrated with Voice, why did I get a message in Hangouts saying I should switch to Messenger? Is it just to pull people who don't have Voice over to an app that's specifically meant for local texting only?
Messenger is an SMS application. It can be used to send SMS. Every SMS that are sent from your device are stored somewhere. Other SMS apps can read and write them.

Phone is a phone app. It is used to make phone calls. Every calls made from your device are logged somewhere. Other phone apps can read and write to this list.

Hangouts
is a messaging platform. It uses your
Google+
account to send messages to other Hangouts users via their
Gmail
address. You can also make video calls with it. It is very similar to
Skype.
However, it is also an SMS app! It can send SMS via your phone number and receive messages from other phones.

Hangouts Dialer is a phone app that acts as a plugin to Hangouts. It enables Hangouts to send calls to other phones via your phone number.

The interaction is simple : Your SMS are logged somewhere on your phone and only your default SMS app can access them. This is why some, but not all, messages are displayed in Messenger when you actually sent them from Hangouts.

If you want every messages to be inside the same app, the obvious solution is to keep Hangouts as the default SMS app. However, don't forget to link your contacts infos in
Contacts.