Federal Rule of Evidence 901(b)(5) and comparable State rules allow identification of a person's voice -- they allow identification of a speaker -- by a lay witness who has heard the purported speaker's voice on another occasion.

United States v. Vartanian, 245 F.3d 609, 614 (6th Cir. 2001) (upholding trial court's admission of a witness's prior testimony in a civil action for violation of civil rights because it fell squarely within the....The hearsay exception for prior testimony applies in a criminal trial or proceeding only if the prior testimony was given against the person who is now the defendant in the criminal proceeding or trial.

United States v. Reyes, 362 F.3d 536, 540 (8th Cir. 2004) (upholding trial court's admission of a co-conspirator's statements as recounted by an agent which did not violate defendant's Confrontation Clause rights....If a statement is offered against a criminal defendant as the statement of the defendant's co-conspirator which was made during and in furtherance, the statement is not a "testimonial" statement for purposes of the right of confrontation guaranteed by the Sixth Amendment of the United States Constitution and the statement is therefore not subject to the constraints on admissibility imposed by that confrontation right on "testimonial" hearsay statements.

Fed. R. Evid. 401 advisory committee's note ("The fact to which the evidence is directed need not be in dispute. While situations will arise which call for the exclusion of evidence offered to prove a point conceded by the opponent, the ruling should be made on the basis of such considerations as waste of time and undue prejudice (see Rule...Evidence that is relevant to a material fact is relevant for purposes of Federal Rule of Evidence 401 and the federal law of evidence even though the material fact is undisputed.