They always say that. It's almost never true. The only 2 reasons cops could enter your house without your permission are:
1-Legally obtained warrant;
2-They have reasons to believe that a crime is being commited or that someone is in immediate danger.*
In case of a 911 call, #2 is playable, but hardly. It all depends on circumstances. Suppose they call you back on the BB and you say "Well, I'm in germany and this is an ip-phone linked to a canada number, so canada's 911 is getting the call, but I'm 7000 miles away". Then what are they gonna do? Break the door to make sure nothing is going on?
A cop can't enter your house, ask you to empty your pocket or show Ids at his will. We don't live in a police state. Without due process or suspicion that a crime is being commited, a cop's job is to get near a highway and go after law abiding citizens driving 1kmph over the speed limit to give them speed tickets. Even if you know for a fact that some dude stole your possession, have seen (or even recorded him) enter his house with your possession, a cop can't enter his house without a warrant. And they will not bother getting a warrant for John Doe's laptop computer or lawnmower. They'll just tell you to stick it, call your insurer.
*Cops will often use this excuse when they've entered a place illegally. Most people don't complain, just like in the case of this cattle prod, but almost everytime someone does file a complain, the cops in questions are found to have acted illegally. The punishment is always ridiculous, usually a simple reprimend. Sometimes a day or a few day of suspension, which is just another word for unpaid vacation.