It was 20 years ago when a pair of businessmen named Bill McGowan and Jack Goken started a little company called Microwave Communications Inc. that was built around a certifiably crazy idea: Somebody could profitably compete in the long-distance telephone business against the world's mightiest telecommunications behemoth, AT&T.

At the time, AT&T seemed impregnable. The Bell System owned about 99 percent of the nation's telephone cable and more than 99 percent of the long-distance business. Shielded by the concept of "natural monopoly" -- the idea that nature had designed the world so that there could only be one telephone company -- the Bell System was legally protected from competition by government at every level.

Indeed, McGowan recalled not long ago, one of the first things Microwave Communications did was to set up field offices in more than two dozen states -- not because it had the business to support those offices, but because presence in all those states made the company a constituent of more than half the members of the U.S. Senate. Over time, McGowan and his company prevailed in the political battles required to make the crazy idea work. Today, McGowan's company, its name shortened to MCI, is a major player in a fiercely competitive long-distance market, and the notion of a "natural monopoly" for long-distance calls has been tossed into history's trash bin.

When the personal computer revolution began to spread across the country a few years ago, McGowan and his engineers latched onto another visionary idea -- a concept that might prove as powerful as their first one. They created an international instant-mail service -- a sort of personalized post office -- accessible at a bargain price to anybody who has a personal computer, a modem and a telephone.

"MCI Mail" lets you set up your own post office, Western Union, Telex and Federal Express operation on your desk-top. You can use it to send letters anywhere in the world at high speed and a reasonable cost. It is an enormous boon to the procrastinator in all of us.

MCI Mail will deliver a screen-to-screen message (text, data, graphics or a complete spreadsheet containing all of the above) to another computer anywhere in the world just about instantly. This "instant mail" service is cheap: In the United States, a note up to 500 characters (about two paragraphs) costs 45 cents. A document containing up to 7,500 characters (about three pages of typed text) costs $1, with a dollar added on for each additional 7,500 characters.

There are other electronic data bases that permit subscribers to exchange electronic messages with other subscribers. But the genius of MCI Mail is that it permits you to go beyond the MCI Mail subscriber base and send a fast letter to anybody in the world.

For one thing, MCI Mail ties in to Compuserve and some other electronic message services, so your MCI Mail letter can be routed to hundreds of thousands of computer users who haven't signed up with MCI. Beyond that, MCI Mail can reach any Telex address in the world.

Beyond that, the service also extends to those benighted folks who don't yet have access to a personal computer. MCI will turn your electronic message into that low-tech relic, the printed letter. You can have your letter delivered to anybody, either on MCI Mail's own stationery, which looks something like a telegram, or on a facsimile of your own letterhead, which MCI Mail will print up complete with a facsimile of your signature.

For $2 for the first three pages, your letter will be printed and delivered via U.S. mail; because it is printed somewhere near the recipient's local post office, this often means next-day delivery. For $9, MCI will guarantee overnight delivery. For $30, the letter will be printed and delivered by courier within four hours of your sending it.

MCI Mail is not the easiest system to use; unless you've read the manual fairly carefully, you could easily get lost in the chain of menus and commands that greets you when you sign on. And since the 100,000 subscribers mainly are businesses, you don't get much of the friendly personal chatter that shows up in electronic mailboxes on systems like CompuServe or the Source.

A year's membership in MCI Mail costs $18. You then pay extra for every electronic letter you send, except that your initial $18 is used to offset mailing fees for the first two months. The membership includes a free subscription to the Dow-Jones News Service, a useful electronic data base.

I know that some of you know about this service already because I get a good number of MCI Mail letters about this column. If the concept of "electronic mail" is new to you, however, you might want to give it a try. If nothing else, that would make it easier for you to send in those letters telling me this column is a bunch of baloney.