Regroup provides analytical reports for Voice Alerts to find out specifics on how well your message was received.
Navigate to "Reports" which you will see in the top tool bar.
From the reports page, click on Standard Posts and then the title of the message results you would like to see:
At the top of the page is a graphical representation of results:
And if you scroll down, you will see detailed summaries of email, text and voice at the bottom: