The Default Text app on the Nexus 5 is Google Hangouts. At first a little hesitant to use it as my default app for text messaging, But after using it im all in, I will now be using it all the time, It is one spot for all your Google chat and text messages fused together in one screen with a gui that is clean and easy to use. You can even set the notification sound on the SMS and Google chat to different tones so you know what type of message you got when it comes in. For a guide on how to set it up and use it is here.
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