I live with somebody who interrupts diatribes against AT&T with a little speech about what convenient and reliable service we have in this country, at prices so much cheaper than abroad. . . .

He has never seen the inside of a PhoneCenter Store, Ma Bell's latest defense of her strangehold on phone service.

If you've called your telephone business office lately about moving, or in any way changing your telephone service, chances are your sales rep (whose training manual says to do so) recommended that you go to a PhoneCenter Store to get fuller answers to your questions, to see the complete line of instruments available, and to pick up your own phone, thereby reducing the cost of starting your new service.

The phone company is gradually converting all residential service to the modular jack system, which allows you not only to carry a phone from one room to another (among rooms that have jacks), but from one home to another. Under the new set-up, once a home is fitted with jacks, there's no need for an installer to come to the house; service is started and terminated from a central office.

What the service reps often fail to make clear is thhat you do not have to go to the PhoneCenter to get service.

Repeat, you do not have to go to the PhoneCenter to get service.

When a service rep trainee implied recently that we could not transact business over the telephone, we had to work our way up -- somewhat belligerently -- to a supervisor, before someome admitted that we could have standard non-Snoopy, non-Flip-Phone telephones delivered to our home -- at a cost so slight ($2.80 per phone) that few people I know would have thought twice about paying it.

I don't feel the least bit ashamed at this small luxury, having talked with a friend whose service rep also led her to believe that she had no choice but to schlepp out to the local shopping center and pick up her own equipment:

"It was ghastly. First, I had to sign up with a receptionist who looked like a go-go dancer surrounded by plastic telephones. And then we had to wait, and wait, and wait, while the 'consultants' talked to other customers. I was there at least half an hour, with two small and restless children. I didn't want to 'consult'; I just wanted two phones, plain black if I could get them."

The slick retail atmosphere of the PhoneCenter Stores seems unsuitable in a public monopoly, but when you think about it, it's only a new manifestation of an old company ploy, which is to get you to sign up for fancier equipment and services than you need. In the past, this has been done over the telephone.

Faster doubletalk I never heard than the smooth patter of a sales rep who convinced me that the only thing that would save my overladen night table was an itsy-bitsy Princess telephone. At the time, it seemed a bargain, as my rep talked of the one-time fee that would entitle me to a Princess phone for the rest of my life, no matter where I moved within the Bell system. A year later I realized that I was paying a monthly service charge for the phone in addition to the one-time fee.I still wince at how I was taken in.

One of the murkier aspects of the PhoneCenter operation is the vague illusion it creates that you can buy your own phone there.

You can buy your own phone -- but not from the phone company (with very few exceptions).

What you can buy from the phone company in the Washington area is the shell of a phone; AT&T still owns the inner workings, and they are licensed only to rent those. Why anybody would want to own the shell of a telephone and continue to pay rent on the inner workings, I'm not sure.

Ma Bell is, however, edging into equipment sales. In Maryland, for example, some designer phones (Mickey Mouse rotary, $139, plus $6.95 tax) are available.

The phone company's party line (no pun intended) is that if your non-Bell phone is out of order and they come to fix it, it will cost you $35; if you use a Bell phone, your repairs are free. However, over a 10-year period you'll pay from $90 to $480 a phone for this privilege, at current prices. And telephones are simple devices that don't break down very often; most repair problems involve damage not to the phones but to the lines, and the phone company is still responsible for those.

Generally, the phone company can tell you if it's a line problem without ever coming to your home, and if they suspect the problem is in the phone you can find out simply enough by unplugging one phone and seeing if the problem remains. Most phones sold on the open market come with a one-year warranty, and many private phone stores offer repair service at flat rate of $12 to $15, plus the cost of parts, the most expensive of which might be the pushbutton pad, which costs about $35.

With thhe money you save purchasing a single phone, you could simply replace a nonfunctioning phone -- as often as four or five times over a 10-year period.

In much the same way that the electric company once insisted that only it could provide the public with safe lightbulbs, so for years the phone company has insisted that non-Bell "terminal equipment" (things like telephones and telephone answering machines) might muck up the system.

Although for some time now it has been possible to buy one's own telephones, until 5 years ago it was illegal to install them without a "protective device" -- a device provided by Bell, at a monthly rent high enough to make owning your own equipment uneconomical. In 1975, the Federal Communications Commission ruled that you could use your own equipment without using Bell's protective device; two years later the Supreme Court upheld the FCC ruling.

Since then the field has been clear for vendors of FCC-approved equipment.