Hate to say it but I am a current but not to renew Vestalink customer and I had issues with voice mail. I fixed it at least for a while by deleting my OBi200 from OBiTALK and doing a factory reset with ***81 and starting over. I had issues of people hanging up the phone, but the voice mail connection ran on a number of minutes. I had evidence in my call logs that someone called and the connection lasted the full time they thought they were leaving a voice mail, but none was left. I had other VM issues to, but the reset helped. At one time I could not even able/disable VM in my Vestalink portal, but after the reset that worked again.
I came not to trust their VM system and got out my stand alone box for VM. Good Luck.