if you hold a o2 payg sim card you can get 500 free anytime mins per month to 1 nominated o2 number
call 2202 from your handset and pick option 3,option 3,option 1 and option 3 to hear about how it works.it is called the one Promotion.
all they ask in return is for your normal £10 min top-up per month
to have the service added to your sim you have to register for it before the 30th of september.
iv looked on the o2 site and can find no details about it.but it does work i have had it on my phone now for the last 2 weeks