I use maven to copy the files automatically.
However, you absolutely have to make use of the Super Dev Mode (http://www.gwtproject.org/articles/superdevmode.html), so that you can test code changes immediately in the phone or emulator!
(As compared copying, packaging and installing a new app every time.)
If you make use of Super Dev Mode, Cordova/GWT development can be very powerful and efficient.
For convenience this is the maven pom config I use for copying GWT code into my cordova app dir:
<!-- copy to cordova app www -->
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>2.5</version>
<executions>
<execution>
<id>copy-resources</id>
<!-- here the phase you need -->
<phase>package</phase>
<goals>
<goal>copy-resources</goal>
</goals>
<configuration>
<outputDirectory>${project.basedir}/${app.dir.name}/www</outputDirectory>
<resources>
<!-- !!! note: filtering corrupts binary files (e.g. mp3) - exclude them if filters needed -->
<resource>
<directory>${project.basedir}/src/main/app</directory>
<filtering>true</filtering>
<includes>
<include>*/**</include>
</includes>
</resource>
<resource>
<directory>${project.build.directory}/${project.build.finalName}</directory>
<filtering>false</filtering>
<includes>
<include>${app.gwt.module}/**</include>
</includes>
</resource>
</resources>
</configuration>
</execution>
</executions>
</plugin>