My workplace sends voicemails as a file to your email when you miss a call. How does etiquette differ when forwarding emails versus voicemail? For example, could I forward the voicemail to another colleague?
It's hard to answer communication etiquette questions, because it depends somewhat on the culture in a particular employer.
That said, one thing that's common in most modern workplaces is a lack of time - people are busy! With that in mind, any time I am personally faced with a communication protocol question like this, I ask myself: what's the most efficient manner in which I can communicate the need-to-know information to my intended audience?
To put that in the context of your question, voicemail can be frustrating, because there's no way to "skim" like you can when reading text. You're stuck listening to the other person for the entire length of the message, whether it's a 5 second Tell everyone, we are going to close the Johnson deal! or a three minute ramble of um and so anyways... that eventually results in the same actual message being communicated.
There's also a potential convenience and privacy question at hand. Voicemails on a computer (versus in a phone system) are pretty hard to keep private if you don't have headphones handy. Especially in an open office environment, it can be annoying for someone to be broadcasting a voicemail for everyone to hear - not to mention the potential for private information to be unintentionally leaked. If all you have is an audio file attached to an email, it's not obvious if it's private or not.
So - unless it is critical that the other party actually has access to the intact recording, it's probably better to summarize in text, versus forward the actual audio recording. This also gives you the chance to link the message to whatever it is you need to communicate to, or ask of, the other person. You could try,
Hey Sam, I just got this VM from Bob - he wants us to close the Johnson deal. Please send over the contract.
That's efficient and direct, and removes the question of voicemail audio files being forwarded in emails.