On Dec 11th 2003 the law changed in relation to unsolicited electronic communications.

Any message that you send must have an explicit 'opt in' requirement - this includes text, voice, sound and images. It includes any of these sent over a public network, which can be stored in a recipient's terminal equipment - specifically, this includes SMS.

There are certain exceptions to this. For example, if the data you hold on a person is obtained in the course of a sale or product service, negotiations for sale or they are an existing customer and the marketing relates to a similar service, then you may market them in this way.

Obviously this is a guide and does not constitute full legal documentation or advice. For more information regarding recent legislation visit http://www.hmso.gov.uk/si/si2003/20032426.htm.