An Arriva Yorkshire bus from Castleford depot which hasn't had its posters changed for years still displays the following contact details: "Call us on 0870 20 10 88. Calls charged at local rates"!
Needless to say, they migrated to 0844 ages ago.

Interestingly Arriva Bus covers the cost of writing to it by providing Freepost addresses for its two Customer Services offices, whereas if you want to speak to someone on the phone, you have to pay it a fee (by use of the 0844 number).