any o2 tariff activated before 27/4/07 includes inclusive mins to 0870, 0800, 0844, 0845 so although its not technically free you dont pay unless u've used ya minutes.
any tariff change after 27/4/07 has completely free access to CS either from the 202 number from mobile of by calling 0870 CS number from mobile, whichever is relevant for your CS dept. however, any other numbers 0870, 0800, 0844 and 0845 will now all be chargeable and not included in free mins.
a bit crap i agree but i guess they're just following where all the other companies went along time ago.