Yea, I thought about that as I used to do the very same thing in VB6. But I had a backgrounder app that would launch and the main app would kill the current VB6 process, open an inet control and download the app into a temp folder and reinstall. Then the backgrounder app would close and open the main app.
But the concern I have, is I dont think you have that much "freedom" in android unless it was rooted. So i would almost need a service that downloads the APK from the server, and requests the install. So the user clicks the install button as normal in android, and the main app closes, install, and reopens the app.
Same thing B4A bridge does I guess.
But in the case of android, i could use the httputils control to fetch the version.txt?