Can a voicemail be grounds to accuse them of unearn and reported income?

This depends on who you are attempting to report the unearned income to and why. Because you posted this question in the tax section, I am assuming you intend to report someone's unearned income to the Alabama Department of Revenue or I.R.S. Generally speaking, they are going to want documentation of earned income, such as images of processed checks, bank statements, or wage earning statements. A voicemail in which someone verbally indicates that money was or will be received/sent does not prove that the money was actually received/sent.