If you're a good friend of mine and your life is in danger of COURSE you can leave me a voicemail. Are you kidding? Time is of the essence! In fact, I'll not only allow it I'll ENCOURAGE you to do so, because the fact you did will seem so strange my natural inclination will be to assume something has gone terribly wrong.
If I haven't responded to your texts, your emails, your Facebook messages, your Tweets, OR your phone calls and it's been more than two weeks, something is definitely up. In a case like that, by all MEANS leave me a voicemail because I've got some serious explaining to do, at the least. Still though, let's keep it short and sweet because if I really have been captured/kidnapped, my patience will have been tested enough as is.
If your call meets every single one of those conditions EXACTLY AS THEY ARE WRITTEN, I'm fine with you leaving a voicemail. In fact, if you can frame the message in a way that I don't have to call you back after I listen to it, you're pretty much my hero. Just keep in mind there is a time limit and if you have to call back to leave a second voicemail there is literally a 0% chance I'll play it.
If you're calling from the past on some top secret time-travel phone the world still doesn't know even exists yet, I'd be more than happy to receive your voicemail. That way, I can have an engineer call you back to explain how texting works.
One 90-second voicemail about something you could have just as easily texted me ought to do the trick. I would say so long at this point but then YOU'D PROBABLY TRY TO CALL ME.