If you have held AT&T stock continuously since 1983 then you owned the stock prior to the original divestiture, which means that you also received stock in the "baby bells" on 1/1/1984. This includes the original NYNEX and BellAtlantics - which later merged into Verizon; BellSouth - which later merged with AT&T, Southwestern Bell and Ameritech - which merged into SBC which later bought the old AT&T, Qwest and Pac Bell, which were also made part of SBC. You also received Lucent stock when it was spun out in 1996, which in turn spun out Avaya and Agere in 2000, and you should also have some NCR stock from its spin out. So whatever purchase price you paid in 1983 for the AT&T stock needs to be reduced by the values of all these spin-offs.
There's some good info on AT&T tax basis here:
AT&T Stockholder Services
Basically you multiply your original cost basis by 0.949 to account for all these puts and takes and stock splits.
Here is a web site with historical AT&T Inc stock price info, going back to 1928:
Historical Stock Data
Linear Mode
