Currently, when maven build is triggered, you can not notify external resources when phase started/ended and same for plugin.

Having a framework to register listeners can solve this issue.

Here is an initial interface I thought can help:

For plugin listener, it would be nice to pass also the plugin's configuration as input. 

public interface MavenPluginListener {
    void onPluginStart();
    void onPluginEnd();
}

For phase listener:

public interface MavenPhaseListener {
    void onPhaseStart();
    void onPhaseEnd(int status);
}

 Registration should be done from pom.xml file, either as part of plugin configuration or in a separate section.