Many users will not have taken the time to read Giffgaff's terms and Conditions. Being someone with no life I have plenty of time to do such a thing. One thing may Giffgaffers will not know is that they have signed up to telemarketing and such things. This is mentioned here:
"18.2. You also agree to the information described in clause 18.1 being used, analysed and assessed by us, and the other parties identified in clause 18.1 and selected third parties for marketing purposes including amongst other things to identify and offer you by phone, post, the Network, your mobile phone, email, text (SMS), media messaging, automated dialling equipment or other means, any further products, services and offers which we think might interest you. If you do not wish your details to be used for marketing purposes, please e-mail The Data Controller at, datacontroller@giffgaff.com stating your full name, address and mobile phone number. Your information is treated in accordance with our Privacy Policy." I have bolded what I consider to be the important sentence.
My idea is provide a large Opt Out Button on the member's Home Page which will permit users to opt out of this "Marketing". It could collate and forward all the information required by Giffgaff's Data Controller. Giffgaff should be more open about this sort of thing and one way of doing this is to add that button.