The tenfold softphone uses the industry standard SIP Notify’s Message-Account property as what is called when the voicemail button is pressed.
If the voicemail button isn’t working, it’s most likely an issue on your providers side.
With one provider based on asterisk, they told us this is what they needed to do to fix it.
This option sets the dialplan extension to reach the voicemailbox, and will be sent in the Message-Account section of the MWI NOTIFY message. Set this if your SIP device supports the Message-Account setting. This option defaults to asterisk:
If you’re savvy with packet captures, here’s what to look for: