Hi, Hank.
Congratulations! And condolences.
Just two days ago I answered a related question here (see: Corp. acquisition recording transactions question.) about AT&T's acquisition of BellSouth. In the process, I found this web page, which should lead you to what you need:
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Click the button under Cost Basis Worksheets for AT&T Corp. shares.
Oh, that it were really that simple! Since your certificate predates the
1984 breakup, you probably should start on this page:
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Note the subtle but very significant difference between "AT&T Inc." and "AT&T Corp." "Corp." was the 100+ year old company that went through the divestiture in 1984, then survived until 2005. "Inc." is the new name for the former Southwestern Bell Corporation (SBC), which was spun off from Corp. in 1984, but then bought Corp. in 2005 and changed its own name from SBC to AT&T Inc. The "Corp." name disappeared in the 2005 transaction - but that was the company whose share certificate you now hold.
Your problem involves calculating the current basis of the AT&T Inc. shares represented by that certificate, of course. But you also must determine what happened to the shares of Ameritech, BellSouth, NYNEX, SBC, etc., that should have been received in 1984! None of those shares have been sold, obviously. Your one certificate now represents shares in all those former subsidiaries. But it gets worse, because each of those companies went through splits, spin-offs and mergers during the 23 years after 1/1/84. For example, your certificate represents ownership of some number of shares of Lucent, NCR, Comcast and many other corporations. The "basis" of each of those shares relates back to the basis in that original AT&T Corp. certificate, and the basis of that certificate today must be reduced by each of the spun-off securities.
If that certificate is for a million shares, you can afford to hire a pro to do all this. If it is for just one 1966 share, it probably is worth a lot today, but not enough to pay a pro, so you'll have to do it all yourself. But the same steps are required for one share as for a million. Maybe the accumulated dividends (including proceeds from sales of fractional shares) will make it worthwhile!
The good news is that there were millions of AT&T shareholders, and many of them were "widows and orphans" who had tucked away their shares and forgot about them. Old certificates still turn up fairly often, I suspect, and there probably are pros who make a career of helping people like yourself who get stuck with the problem. Ask your broker (not the young kid who went to work there last year, but the grey-haired old guy who has been there forever and is about to retire). Don't ask him to figure it out; just ask whom you should contact. I'm sure that AT&T itself has a crew that works full-time on these problems. That is the crew that works behind that web page.
If this share is part of the estate of a deceased person, your job may be cut in half. Inherited shares usually get a new tax basis and holding period based on their fair market value at the date of death of the owner. So you don't have to track down the original basis and do all the math to apportion it to today's holdings. But you do still need to gather up all the shares and fractional shares that should have been received over the years and value those at date of death. Then, if the death was not very recent, you will need to track developments since the death.
Good luck, Hank. And please let us know what you find out!
RC