I have a Galaxy S4 and am unable to play the voicemail files that are emailed to my phone. What specific app do I need?
Any audio player is suitable to play voicemails as long as they're in the proper format. You can browse the Play Store to install an audio/video player to play your voicemails. I can recommend you to install MXPlayer as it's an all around free solution to play audio/video files.