The May 1982 issue of BSTJ has a seires of articles on voice storage. This technology led to voice mail services.
As usual, Bell Labs extensively researched the architecture, physical design, software, office engineering, maintenance, and reliability, with articles describing in detail the findings.
The preface says the FCC ordered Bell to cease work on this system as it violated regulatory policy--it was considered a premium add-on in violation of "Computer II". So even though in 1982 Bell's competitors were providing both transmission services and customer equipment, Bell was forbidden to offer its own premium services.
How much of this research carried forward to voice mail systems I don't know. But I can't but suspect that subsequent private developers benefited from Bell's original research and trials.
table of contents may be found at: