I recieved a text message from 3 offering free spotify premium for one month. It can be cancelled straight away so no payments will be taken.
To get this deal go to http://mobile1.three.co.uk/sdf/spotify
on your 3 mobile. You must connect to this though the 3 access point and not wifi. If you don't have a data plan this should still be free as it is there own site. Click the big get spotify premium link, which takes you to another page where you have to press another get spotify premium button.
To cancel simply go to http://mobile.three.co.uk/personalise/spotify/unsubscribe
again you need to do this on your phone.