If the calls are threatening, abusive, or obscene, report them to the police and your service provider. Note down the date, time, and number that called, along with any other useful information. Most providers offer products, services, and advice to help you screen or block such calls. Some silent calls are generated by automatic dialling equipment in call centres, where the number of calls made outnumber the operators. To prevent this, register your number free with the Telephone Preference Service (TPS).