Today you do not need to worry, if the phone is no longer have internet connection
with "Find my phone " you could find your phone even without internet.
If you try to find your phone with internet and you cannot reach it you could use offline mode to find it using SMS.
Find my phone or track my family .
this app allows you to find your phone when you miss it by using another phone.
this app use GPS and SMS it doesn't need internet to find your phone.
also its allows you to track many phones, and allows many person to track you.
also its allows you to ask help from all your tracking persons.
-Wheres My Droid
-Android Device Manager
-NoteThe project is open source here