You should join www.captain69.co.uk and you can then post ad on their escort board for free.  They also have paid for banner ads.  It's a great site and definitely the best place to advertise.  I disagree with the previous poster (whom I hope was joking!), advertising in phone boxes is for the lower ends of the market - and it's illegal so if you get caught sticking up your cards you are in trouble!  Message me if you want any further info - I might ask you to return the favour as I'm visiting NYC next month