If your telephone service is supplied by the Bell System, I have good news for you. Also bad news.

For a long time, it was the policy of Bell System companies to rent their equipment to customers. Ma Bell would not sell you a telephone.

In recent years, Bell companies began selling their Design Line telephone shells -- the housing only. The insides (the working portion of the telephone) remained the property of the company.

Those who ordered an ordinary phone paid $1.10 a month for leasing the instrument, and the phone company kept it in working order at no extra charge. Those who bought the shell of a Design Line phone also paid $1.10 a month in rental, and they also received free service if the phone malfunctioned.

Now the Bell System has decided to stop charging rent on the innards of Design Line phones. When you buy a phone from Ma Bell, you'll buy the whole thing and will be permitted to use it wherever you wish without paying rent on the instrument itself. That's the good news. The bad news is that you'll pay more (from $69 to $100 more) to buy the telephone, and if it develops any ailments you'll have to pay for fixing them unless you have purchased a maintenance contract (for $25 a year or less).

If you already, own the shell of a Design Line phone, you will be given the option of buying the working parts too or continuing to pay a monthly rental fee. Henceforth, however, no additional customers will be accepted on the old buy-the-outside-rent-the-inside arrangement.

Janice McDonald, product manager at C&P headquarters, says that the change in policy is "an obvious move for the Bell System." She says, "If we want to be a retailer, we must have something we can sell outright. We're heading into an unregulated market and this is a logical first step in that direction. Now when a customer buys a phone, he can do anything he wants with it -- just as if he was buying a toaster or a television set."

If you're wondering whether the new or the old arrangement is the better buy, consider this:

By buying your own phone, you will save $1.10 a month or $13.20 a year. Divide that $13.20 into the amount you must pay for the Design Line phonee you select and you'll know how many years of trouble-free service you'll have to get out of the instrument before your investment has paid for itself.

P. S.: Under the new sales arrangement, most phones purchased by customers will carry a one-year warranty. If these instruments measure up to AT&T's usual standards of quality and reliability, a maintenance contract should be superfluous.

On the other hand, if you're clumsy enough to drop phones or unlucky enough to buy a lemon, you might end up wishing you had never abandoned the old system of leasing the equipment and letting Ma Bell worry about keeping it in good repair. LITTLE WOMEN, BIG WOMEN

In a recent column about supermarket loading lanes, I said the help given by attendants was appreciated especially by 95-pound women who have nobody to help them unload their purchases when they got home.

Gladys N. Lee of Silver Spring responded: "All right, that did it. I was born big. I'm 5 feet 10 and all my life I've heard, 'Let Gladys do it.'

"While I and my weak back struggled to move an office typewriter, for example, there would be six men hovering over Grace to help her. She was 5 feet 2 but strong as an ox. The little ladies get all the help while the big gals have to haul away.

"I'm the next sentence you refer to lifting heavy items like canned goods, bottled goods and meat. Really, Bill!

"That does not apply to very many of us, big or little. Who on earth can afford to buy enough meat to be too heavy to carry? Ask your roommate.

"Excuse the longhand. My typewriter doesn't work and I'm waiting for my 95-pound daughter-in-law to put it in the car for me."

Gladys, if I mentioned meat prices to my roommate, I'd have to listen to a 20-minute denunciation of cattle growers, supermarket wage and price policies, Congress, Reagan, Carter, Ford, Nixon, Johnson, Kennedy and Eisenhower. (Harry Truman was the last one she liked.)

I was thinking about the weight of the meat she pays for, not the weight of what ends up on the table after the bones, fat and gristle are subtracted.