In 50 ways to save money article Telegraph say

"28. Call premium phone lines from your landline. 0800 numbers will be free to call from mobiles in 2015, announced Ofcom last week. However, until that time comes, make all calls to premium rate numbers from your landline, as this is either free, or much cheaper. Calling 0871, 0872 or 0873 from a landline costs between 5p and 12.5p per minute from a landline and between 25p and 41p from a mobile. Calling 090 numbers cost between 10p and £1.65 a minute from a landline and up to £2.55 a minute from a mobile."

http://www.telegraph.co.uk/finance/personalfinance/consumertips/10522665/50-ways...

No mention of service charge. No mention of looking for alternatives. Appear to be classing 0800 numbers as premium rate calls.