Power the device off then back on, and then dial *228 send and option 1 on the device.
Then try dialing *86 or dialing your own number area code first to access voicemail.
Enter your password, and listen to all the messages. Delete unwanted messages.
If you still can not access voicemail, ensure that you have the Basic Voicemail feature on your account by logging into your My Verizon Account online, then going to the Shop Tab, then Change Features, then view your current features.
I am getting a busy signal when I try to access my voicemail. I tried what you said and it still does it. I logged in to my account and it says voicemail is included. I've had my phone for a while and didn't activate the voicemail when I got it, and I've seen that it says it is cancelled after so many days. I was wondering how I can get it reactivated, if that is what is causing the problem. I have a prepaid phone account and a Samsung sch-u350 phone.