I've just renewed my mobile contract with Vodafone to get their One Net Express package. It gives you up to 5 different geographic landline numbers that all terminate on your mobile (different area codes) and when you call customers, you can display the landline number as the outgoing caller ID. A big benefit has to be no call forwarding charges from a fixed landline.
You can also call 0800, 0845 and 0870 with no extra charge and you get all inclusive landline and mobile calls. £55 a month has to be worth it!