Android 4.4 is going to be kind to those prolific developers with those third party SMS apps. It is great that you can have your choice when it comes to using a certain messaging app, but sometimes they just are not as stable as they should be. This is due to developers having to use hidden APIs, and side step things on the developer side just to keep their apps running correctly. That will all change in Android 4.4
Google detailed on their blog page that they intend to give developers the actual APIs, which will cause their SMS apps to run beautifully. Users will be able to pick which SMS app they want as default, and those apps will run like the stock messaging app. It is a long time coming, and I am sure those devs out there are happy to here this news. Let us know what you think about about it.
Source: Android Developers