I have permanent London number with Skype, costs $90/year makes it easy to call banks and government offices, $10 call time lasts ages.
I also have a GiffGaff SIM in one of my phones, great for OTA numbers from banks. SIM is free, 10 pounds call time lasts 3-4 years as you need to send SMS every 6 months to keep it active (SMS deducts 30p from your call credit)