Standard CallingPost messages are delivered to a live person or an voicemail if the member does not answer the call.
Straight to Voicemail (SVM) will attempt to deliver the message ONLY to a member's voicemail box, without the option for the member to answer the call live.
From the Additional Phone Message Option Screen:
Click on the Send Calls Straight to Voicemail (SVM) option.
Click Next to finish sending your message.