you will need your phone’s IMEI number for the police and your network provider.
To find this either check your ‘About phone’ in your settings – lots of infomation here, or 
type *#06 # into your phone’s keypad.

You will need to contact your Network provider as soon as possible so that they can block your phone to prevent you getting unauthorised bills.

Fill in these details now and they will be readily available in case you lose or have your phone stolen.