Is this actually a plot hole?
In the Goofs section IMDb has the following listed as a plot hole.
When Marcia Sindell calls Buster up and asks if he has seen or heard anything about Paul Sheldon, he tells her that if he finds anything he will call her right back. Buster wouldn't be able to call her back because she did not give him her phone number, the firm she works for or where she is calling from.
Why wouldn't he be able to call her back? She gave him her name and did say she was calling from New York. If I remember correctly, she also gave her job title. It wouldn't be that hard for him to get her number by calling information.