I don't have landline, but when I call using google phone, instead of getting "Welcome to Verizon Wireless, your call cannot be completed as dialed. Please check the number and dial again. Announcement 4640-7.", google phone will get a standard ring and in the end google phone will say "At (time), (the phone number) was not available for a phone call.
As budone said... sounds like the number has been changed or disconnected either by Verizon or the Caller then selves.
This problem was occurring when someone would call my number and they were transferred to voicemail.
Apparently the forwarding number for voicemail was no longer used so they would get this message.
After working with Verizon technical support they were able to update the forwarding number for voice mail and the problem was resolved. If callers get t his message when being transferred to voice mail you may have the same issue.