(FORTUNE Magazine) – You're talking on the airphone from a plane above the Midwest, planning strategy for a deal that could clinch your promotion. Then the aircraft breaks the ground station's range -- and you're cut off dead. So much for making VP. American Mobile Satellite -- a consortium of eight companies including Hughes Communications and McCaw Space Technologies -- is developing a system to combat the problem. At its heart are satellites that would allow users of mobile phones on land, on sea, or in the air to call clear across the U.S. without service interruption. , With today's cellular phones, you communicate through broadcasting cells, covering about six to ten square miles. If you are traveling, your call is patched from one cell to another, a potential cutoff. The satellites will do away with cells. The system, which involves bouncing signals off the satellites, is scheduled to go into operation by 1993. The standard antenna for car phones will be a plate measuring only four by eight inches that can pick up satellite signals from all directions. But it won't come cheap: $4,000 for the hardware and $70 per month for service, vs. an average $500 and $25 for standard cellular. J.B.B.