There are various types of "nuisance calls", and these can be dealt with in different ways, as outlined below.
The most alarming may be calls involving threats or menacing statements addressed to you or your family. In these cases you should notify the Police immediately: they have the authority to trace calls to establish who is making them.
Obscene phone calls are usually made to women by men selecting phone numbers randomly. As a general preventative measure, it is better that you do not identify yourself or announce your phone number when you answer the phone; it is better to simply say "Hello".
Obscene callers may also often use the phonebook to find numbers of women to harass. It is therefore advisable that women use only their initials, not their full first name or names, in their phonebook entry, and that they do not include titles (Mrs, Miss or Ms) in their entry.
Tactics such as blowing whistles into the phone lose much of their effect in being transmitted over the phone line, and may well encourage or aggravate the caller.
If nuisance phone calls become persistent, you should consider changing your phone number. There is normally a fee for changing your number, but it may be waived if you are changing it because of nuisance calls.
You may also request that your new changed number be unlisted. There is an additional fee for this.
You may also consider arranging a code with the people who are most likely to phone you â€“ for example, arranging with them that they let the phone ring for a set number of rings, then hang up, and then phone again so that you know who is calling.