[Qt-interest] what is event/signal for phone lock/unlock and app going background/foreground?

[franki]

Hello,

I have app which exchange data with server, but when I put the app in 
background or I lock the phone network connection is closed after a while, 
which is generally good, but after unlocking the phone, or calling application 
to the foreground I would like to be notified, to reestablish connection with 
server.
I'm using Nokia N8 and C6 and Qt 4.7.3 on Linux platform. Which event or 
signal should I look for?

best regards
Marek