The process of designing a mobile application has become more streamlined over time. Apple's iOS guidelines are much more straightforward and easier for first-time designers. Similarly Android and Windows Mobile are just as user-friendly offering beautiful interface examples and resources.
The following UI shots are from Dribbble designers who've created unique instant messaging chat applications. These are some of the highest quality interfaces which should provide inspiration to mobile app designers. Whether new or experienced, every designer can glean something magnificent from these mobile interface mockups.