I have gotten my voicemail forwarding back twice now by adding an additional Email address to my account. If you Log onto
http://my.magicjack.com and scroll down to ACCOUNT EMAIL
then click Details you will see:

All accounts are referenced by the email address(es) that you provide. You may add an additional email address to your account or disable an email address that you had previously provided. Each email address is stored with its own password, so we ask you to provide one with the new email address.
MORE INFO:We do require that you always have at least one email address assigned to your account. If you'd like to change your email address, just add the new address and then delete the old one. "Account" signifies the email address that we use when we need to contact you. Even if you have more than one magicJack™ on your account, only one email address is associated with your account. "Voicemail" signifies the email address that our voice messaging service uses to send emails that contain voice messages. This may be different from your account email, but does not need to be different. Each magicJack™ may be configured with a different email address, or the same email address if you prefer.
My voicemail was not forwarding to my email so I opened a new Gmail account and added it to Magicjack
I then assign it to Voice Mail with the Radio Button

provided. I had notifications immediately that I generated by calling my number myself as a test.
Unfortunately this "fix/workaround" only lasted two days and I had to reassign the voicemail to my original email address again today to start getting notifications again. It appears that Magicjack has some problems with their server administration or software. I hope that service is not going to continue to deteriorate.