After installing another SMS app you might be prompted by the app to set it as the default SMS provider. Doing so will allow the app to alert you to new messages, and handle any outgoing messages you compose via another app.
There are times when you either dismiss the prompt on accident, or you're not prompted at all, and thankfully Android 4.4 KitKat includes a system setting to change the default SMS app. Here's where to find it:
- Launch the Settings app on your device, and then tap on "More..." under the Wireless & Networks.
- The second option will then be "Default SMS App." Selecting it will present you with a list of all installed apps that are capable of being set as your default app.
- Select the app you want and go back to messaging away.
On one hand it makes sense why the SMS setting is under Wireless & Networks, since SMS is handled by the network. But on the other hand, I don't really understand it's placement. If anything it should have it's own listing under the Device section in the Settings app.