What is Stand-by Time?
The problem with smartphones is that many are constantly using data, especially a BB which is receiving email every 15 minutes or less, or updating location or whatever. That being the case, it is never in a state of not being used. Plus many devices search for a better signal as you move, using some power.
To be totally in standby and to get close to the advertised standby times, it really should be turned off.