For the people of Kent, the answer would appear to be 999.
Of the 170,000 emergency calls made to Kent constabulary last year only about a quarter had anything to do with the police. The vast bulk were for the trivial, the mundane and the absurd. Many Kent residents also appear to view 999 as a cheap alternative to Directory Enquiries.
The police have finally had enough. In two weeks' time anyone who telephones 999 and asks a detective to inform their mother that they are going to be late home - as someone did earlier this month - will be given a verbal clip round the ear.
The operator will switch the caller onto a pre-recorded message which says: "The 999 service is for emergencies requiring urgent police attendance. Your call does not require urgent police attendance and you may have endangered someone with a genuine emergency."
The 125,000 wasted 999 calls to Kent police last year included:
Requests for the frequencies of local radio stations, and phone numbers for the local Chinese restaurant and the Dorchester Hotel in London.
A caller saying: "My window has just been painted and I cannot shut it. Can the police do it?"
A man who had a stray cat in his house.
A woman who asked the police to turn down her son's stereo.
A pregnant motorist who wanted to know whether she should wear a seat belt.
The police message also gives a number for a free information service. In return for the tens of thousands of calls the company that runs the service is likely to get, they are paying for a pounds 100,000 campaign to publicise Kent's new 999 system.
Supt Robert Chidley, of Kent police, said: "This is the most important campaign we have ever waged. Abuse of the 999 service endangers everyone."
A police source was less diplomatic. "We're fed up of getting hoax calls from lazy and clueless people who are wasting valuable police time and putting lives at risk."