If you are not with 1899
www.bestminutes.co.uk access no 0911 501 15 15 allows you to call them from a landline at 15p a min. However you start paying when you dial the access code,and if you get engaged tone,or they dont answer, your have pay at least a min charge.
If you are not already aware 1899/Best Minutes are part of the same group,and as Dave points out in the OP these calls most be loss leaders.