MTJ packaging support is provided via the Java ME MIDlet Suite project context menu as shown in this snapshot.
If you have more than one configurations in your project, MTJ will ask you if you want packaging for all the configurations as shown in following snapshot.
Package for all configurations will do clean build as many times as how many configurations you have. So if you have too many configurations, it will take a long time to package all configurations. For more information on configurations, refer Configuration Documentation.