waltsailing:
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,
i got your point, but i think it doest work in my project,
because i need to assume that there will have 2 or more lighting dimmer to connect my android phone through arduino board,
if i change the shield as Ethernet, capacities will be the problem.
in my project, i got some idea now,
i used the serial device tester,software, to send hex to the RS232 wireless controller, it's work!
i can turn the light on and off and also the brightness.
but some fuctions do not function. ( i will show it later)
so, in other word, i need the arduino board to send out hex(should it be byte?) through serial port.
i will keep trying my work.
all guys could share your ideas here 
ah... another question, is it possible to directly connect my arduino uno r3 board TX and RX and gnd pin to RS232 serial port pin 2,3 and 5?