The latest in one-upmanship appears to be the installation of a radio-telephone in your car so you can keep in constant touch with your office, or anyone else for that matter. A firm called Carphones seems to be making quite an impact on this market and now have radio-transmitters based at London, Luton and Birmingham, the three areas overlapping to cover quite a proportion of the Home Counties and up to the industrial Midlands. Carphones use ITT equipment which is rented out at £16 per month plus an initial installation fee. This includes a selective calling system whereby, if you are away from your car, your messages are monitored and stored for when you return. Executives who wish to learn more should contact Carphones at 65a Station Road, Chingford E4 7BU, or 61-65 New Street, Birmingham B2 4DU, for a fully illustrated brochure.