Hi,
I just posted a way to do this using a windows phone, no app required, so it should work with the android. The Arduino doesn't need to be connected with a wifi shield. I used the wireless router in the house, just an ethernet shield and a cable. The Arduino serves up a webpage and then it runs the x10 which do the dimming. So, you access the web page from the android and click the buttons. I have put 'dim and brighten', along with a number of x10 on/off command buttons. The thing about x10, you have to select a specific address and then send an on, then you can dim/brighten. Here is the video link. I posted the code in a previous post.
Regards,
Walt,