As far as I understand, it's free. I'm a Barclays customer and they kicked the service off. If you have a smartphone, locate the app, download. You finish off the app & authorisation by going to an atm machine. Quite straightforward to set up. You can also go into the bank and sort the final step out with a member of staff.
I only have a few customers who use it though. I think it's a great idea, but it seems to be slow catching on. People who don't bank with Barclays can also use this system.