0843 numbers are revenue generating numbers that can have varying charges to call them depending upon the provider, my provider (Gradwell) charges about 52 US cents per minute to call this number. You would be better to get a UK 0333 country wide number that is charged at the local rate from anywhere in the UK, have a look at www.gradwell.com, their SIP and IAX2 trunks are very reasonably priced.