"we heard the noise of it over the phone."
Oh my God!
Was your mother-in-law near the Towers?
The co-ops near St Margaret's Senior Center on Fulton Street. About five blocks. Her window faced the BB.
Several days after the towers fell, the London office called the family and told them of the call. He was talking to them. They heard a scream and then the phone went dead.
I think it helped them find some sort of closure because they still have not found any of his remains.