Yes, you can find some free 01 xxx or 02 xxx phone numbers for Sky customer services, but its very fast "die".
Last year i use 0844 995 95 95 phone number for SKY customer service.
It always valid, and cost just 0.05 per minute.
This number for main switchboard - you can use it for all question about Sky - for Sky Customer services, sky tv, sky+,sky+hd, broadband, telephones, new, existing & returning customers & general enquiries.
Sky customer services opening hours
Daily – 8:30am to 11:00pm