0333 & 0330 numbers work in exactly the same way as other non-geographic numbers, except they are cheaper to call, even from mobiles. This is because you (the customer) are just calling a local number no matter where you are calling from in the UK. If you have a contract mobile or landline package with inclusive minutes, 01/02/03 numbers are usually included free.
Still better news, if you need a quick quote and I'm out of the office the call will transfer to my mobile handset at no extra cost to you even if you are calling from a landline, so that I can help you there and then.
03 phone numbers meet the strong and growing public demand to have a recognisable phone number, which both identifies the type of organisation (business) being called and offers a clearly priced call.