Didn't really see this posted anytime recently but it's good-to-know-type information, especially if you're like me and sign up for loads of stuff and include your telephone number in the form.
The Telephone Preference Service (TPS) is a free service. It is the official central opt out register on which you can record your preference not to receive unsolicited sales or marketing calls. It is a legal requirement that all organisations (including charities, voluntary organisations and political parties) do not make such calls to numbers registered on the TPS unless they have your consent to do so.
Organisations with which you have an ongoing relationship, for example those who regard you as a customer, (or in the case of charities - a donor) may well gather your consent during the early stages of your relationship with them and will therefore be entitled to call you even if your number is registered on TPS, unless you have previously told them specifically that you object to them calling you for marketing purposes.
The TPS can accept the registration of mobile telephone numbers, however it is important to note that this will prevent the receipt of marketing voice calls but not SMS (text) messages. If you wish to stop receiving SMS marketing messages, please send an 'opt-out' request to the company involved.
As TPS registration only prevents marketing calls, organisations will still be able to call you for the purposes of genuine market research.