I use an 0845 for mine. It only costs 3.5ppm for a customer to ring but some of them won't know that due to misinformation in the media that seems to lump them in with 0870 numbers.
I paid £200 for usage of the number as it's a more memorable one. I also pay 2.5ppm to receive calls. However, I have never yet exceeded the minimum charge of £2 a month. I know it's a poor deal compared to many out there but I'm tied in unless I want to lose the number that I paid for.
I only got the number in the first place because I thought I was going to be moving house some time back but it didn't happen (and won't now). It would have been a trivial matter to point the 0845 at the new number. So what I am doing now is giving landline, virtual number, and mobile. That way they have a choice of which to phone.
One drawback to having a more memorable number is that it has similarities to the one used by Devon and Cornwall police. I get some pretty odd calls on a regular basis

- including a voice mail message from a probation officer stating someone's name and address which was meant to be confidential - oops!! I did actually reply to that one as it sounded urgent.