The direct to voicemail transfer already works with grandstream devices using * * then the extension exclusively during transfers.

It also works for accounts that have it added by request where 9101 goes to extension 101's voicemail.

In both of the above cases there's no voicemail greeting announced. Just a beep. This can confuse clients. Often times those messages include afterhours, rules, or special means of contact for clients.

Voicemail greetings playing when direct to vm transfers are made is a useful feature needed.