If someone calls your Another Number and the conditions busy, no answer and unavailable are met then the call will go to voicemail. Voicemails that you receive will be transcribed into text (if quality allows) and will appear in the 'Recent' tab of the Another Number app.
There are two options when it comes to forwarding to voicemail.
1. The standard way is to let the call ring on your phone before diverting to voicemail. You will see the incoming call, let this ring through to voicemail, if you decline the call there is a possibility that your carrier will pick up the call sending the call to your carriers voicemail system.
2. Forward calls straight to voicemail via enabling the 'Do Not Disturb' mode, calls to Another Number will be sent directly to voicemail and your phone will not ring: