First few times I created the .apk with appmobi I also had a blank screen after the loading screen. I removed the appmobi script from my html file and that got it working.
Thanks for letting us know how you got it working AndyWatson. I removed the script and it worked. I now have sound <img src="smileys/smiley4.gif" border="0" align="middle" />
I haven't tried it yet but you should be able to change your app version number form 3.4.0 to whatever version you want by opening your folder were all your appMobi demos are stored. Then search for your app project folder, open it, and rename the 3.4.0 folder to whatever version you want.
Let us know if you have any luck this weekend with modifying phonegap.