To expand on my rather too concise reply earlier
As a rule, if I can't call on 01/02/03/080, I don't deal with the company at all and so they lose business (I must admit to liking the challenge of finding an alternative number, however
).
I see use of 08s as either:
cynical revenue gathering
ignorance (i.e. a small business might really think they're providing a service, unaware of the cost to their customers)
disguise (why don't they want us to know their call centre is in, e.g. Sunderland?)
I also have my own 0844 number that I give as a contact number to such companies if I feel that they are too blatant in their use of 08s (ironically, the Halifax Bank web site rejected it as not a proper number, even though all their contacts are 08s). Sad or what?