I got an email from a friend today, and almost didn’t bother to read it, as it started “Zingo Taxis: IMPORTANT INFO”. But I did, and actually it sounds like a good service. When you’re in London and want a cab, you ring Zingo and they automatically connect to you the nearest for hire taxi (they use GPS based on your phone signal) who will then come and collect you wherever you are. It costs £1.60 on top of the usual rate, and I can certainly think of times when I’d have been glad to do this.
The BBC did a review of this service in April, and a quick look at google also supports this as being a genuine service and not some form of spam.