Phone doesn't respond to ping
I believe this is simply because Android puts the Wifi to sleep to save power when the screen is turned off. You can try setting the Wifi Sleep Policy: Settings &gt; Wireless &amp; Network Setting &gt; Wifi Settings &gt; Press Menu button &gt; Advanced &gt; Wifi sleep policy to Never and see if your problem still persists.

Alternatively though, instead of having your server ping your phone, I think it will be easier for the phone to "ping" (or make a HTTP request or through other methods) the server when it is connecting to your Wifi network. Your application can register to the system to receive a broadcast Intent when certain Wifi events occurred.