I have to say that the people I talk to about telephone numbers have always said it is nice to have a local number, but they would call an 0800 number first if there was to companies together.
I have an 0800 which is not on the van at the moment, only on our leaflets and the response is about the same as the local number. We asked last year where people got our number and very few mentioned our van, most people if they saw me just came up and asked about our services.
Hope this helps