Arduino to/from mobile communication

Here is the basic idea:

mobile device ---> wireless router ----> arduino

The arduino is connected directly to the router by using an Ethernet shield. The mobile device is connected to the router wirelessly.\

The mobile device must be able to send information to the arduino. I would also like the arduino to be able to send information to the mobile device but this is not a priority right now.

I am very new to this and I am mostly doing this for the learning experience. One of the biggest problems I have is how to use an android powered device to send data to the arduino. Is there some sort of app I need?

Any guidance is greatly appreciated.

Thanks in advance.

If an android has browser capability to download a web page, then a number of arduino server examples have been previously posted might be of use. Note that for the android to receive a request from an arduino, the android will need to be running some type of server application.

What about just sending information to the arduino. Basically all I want to do right now is send information to the arduino, not receive.

There was a similar request a few days ago, that I posted an answer listing other ways than just ethernet for an Android phone to communicate to an Arduino: http://arduino.cc/forum/index.php/topic,126680.0.html

Yes. I need to do it via wifi because i need wireless communication. I've tested bluetooth connection and it does not give me the range I need. It only gave me about 40ft and i need over 100ft. I've experimented and came to the conclusion that I need to make use of wifi somehow.