I have been using these for about 5 years now. It costs 2p a min to divert to your landline or 10p to your mobile.
On certain fones like nokia and samsung it actually comes up diverted call so you know its costing you so I usually say i am busy can I call you back.? or I let it go through to voicemail which costs just over a penny.
You can have any area code you like the only problem is now they charge £20 a year now for the number so could be expensive with several numbers.
I bought my numbers outright before they started charging a yearly fee which was a tenner.
I can make £25 top up last nearly a year as I have it diverted to my landline which diverts to my mobile so only incur the 2p a min. I get free call divert to my mobile.
There are still plenty of people out there dont like ringing mobiles from their home phones.
check it out.
http://www.ttnc.co.uk/phone-numbers/01-and-02-numbers/pay-as-you-go/Pauly