The Spectator.co.uk:

"Q. A friend of mine is married to a soldier who thinks of himself as rather 'macho'. The problem is that he has a very effeminate voice, so when I ring my friend I am initially never sure if it is him or her as neither of them gives their name when answering the phone. His macho self-image would not survive being mistaken for a woman, even telephonically. How can I avoid mistakenly confusing him for her?
K.C., Perth, Western Australia

"A. When you telephone this couple, always announce yourself. 'Hello, it's--[here give your Christian name].' If the respondent fails to identify him or herself in response, just carry on probing along the lines of 'How are you today? Have you achieved a lot?' until such time as the activities on which your interlocutor has been engaged have provided sufficient clues to establish their gender"