He can do it by dialing *86 from the device.
I know you can access the voicemails from a landline, but that's once it's set up. I assume when you call him that it just continues to ring or eventually just hangs up? Does it tell you that his voicemail hasn't been activated? You could try and press # if there is a message that chimes in. Otherwise I think he may have to do it himself.
Having the voicemail setup is definitely important. However, you will not be able to set it up for him on a land line. He will need to set up from the phone. Visit http://www.verizonwireless.com/support/knowledge-base-115753/ for instructions.
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