I have my own 0844 number and I give it to firms who will not give me a 01, 02 or 03 contact number.
Customer revenge I call it and the number was free.
First it tries my home 01 number and if that is busy it tranfers to my VOIP.
Reminds me I must change the greeting tune from the christmas theme.
And it gets even better, you know when people withhold their number, well if they do the system sends me an Email with the number that called and its location.