While the billing is different, calls are usually routed the same way they are for a toll-free telephone number, being anywhere despite the area code used.
"Hopefully it will become dangerous to advertise your number in these boxes because you may lose your business.
"If you are a trafficker or pimp all you are interested in is money, you are certainly not interested in the welfare of the women or young girls." Chief executives of all the major mobile operators have been invited to a meeting at City Hall in October.
'Repeat business'"Firstly, they become a source of repeat business.
Plus the numbers operate as a kind of switchboard, there will be several poor girls operating behind the number.
It said geographic telephone numbers “are an increasingly scarce resource”.
The cost of making the calls will not change and there will not be any disruption to services, according to Ofcom.
He said mobile phone numbers were valuable to those behind the sex industry and should be cut off.
The deputy mayor has invited Vodafone, Orange, O2, 3, Virgin and T-Mobile to meet him.
Major mobile phone companies are being urged to help cut the number of prostitutes working in London.