If it's important I'll be expecting a phone call or know who is calling me. All that a voicemail does is tell spammers that they have a valid and active phone number that they should keep calling.
"Hi honey, it's me. I'm calling from the hospital, my phone was damaged in the crash. I know this area code is weird, we were only about halfway to Grandma's when we were hit..."
"Unknown number? I'm not listening to that shit, I'm waiting for my wife to call when she gets to her parents house!"