SINCE Ah Ming bought a tiny scanning machine for $1,300 from a shop in Tsim Sha Tsui he has carried it everywhere. Whether he is waiting for friends in a restaurant or standing in a bus queue, Ah Ming makes sure his machine is scanning the cellular phone radio frequencies between 800 MHz and 1,300 MHz so he doesn't miss out on any interesting private mobile phone conversations. ''Sometimes it is quite boring. You just hear stupid conversations about where people are going to meet. But then sometimes you can find something really good.'' He said he often tuned into people making calls to the soft-porn 173 numbers. ''I get to listen in for nothing,'' he said. Ah Ming has come to think of himself as something of a psychologist. ''Before I had this scanner I imagined that when men talk to their male friends they tell them all about their conquests and successes with women. But I have been surprised. Men just mention these things to each other, while women . . . with women you hear about every intimate detail,'' he said. He said he knew it was illegal to use the scanner for that purpose. ''It's just a bit of fun,'' he said. When asked about how he would feel if he thought other people were listening in on his private conversations, Ah Ming just shrugged. But anyone hoping to overhear an intimate mobile telephone conversation with the Governor, Mr Chris Patten, will probably be disappointed. The Governor's spokesman, Mr Mike Hanson, said Mr Patten rarely used cellular telephones. ''He will sometimes use one to take an urgent message, but he doesn't carry one around with him,'' Mr Hanson said.