Below I can hopefully convince you why certain permissions are used.
This application has access to the following permissions:
Services that cost you money - directly call phone numbers
This permission is used by this application to silence unknown callers.
Hardware controls - change your audio settings
This permission is used to modify the audio state before and after announcing notifications to the user.
Your messages - receive SMS/MMS
This information is required to notify you of incoming SMS/MMS messages.
Your messages - Send SMS
This is required for voice reply.
Your messages - read Gmail
Used to notify you of incoming Gmail messages.
Your personal information - read contact data
This information is required to look up the incoming phone number and compare it against your contacts. Similarly used for SMS, email, Gtalk, etc.
Your personal information - read calendar events
This is used to provide calendar event notifications.
Phone calls - read phone state and identity
This permission is needed to detect who is calling you and when that call is happening.
System tools - prevent device from sleeping
This permission is used for the Shake to stop feature of the application. Also used for SMS voice reply.
Your accounts - discover known accounts
This one allows this application to detect the valid Gmail accounts that you may or may not want to use with voice notifications.
Phone calls - modify phone state
System tools - automatically start at boot
This one is needed for those cases that you allow this application to start on boot up. If you configure this application to do this, then about 30 seconds after the phone boots up, this app will start up.