The Simultaneous Ring feature lets all the incoming calls to simultaneously ring on the pre-specified phone numbers.
No, it's absolutely free to use the Simultaneous Ring feature.
To enable Simultaneous Ring on your AXvoice VoIP plan, sign into your AXvoice online control panel and look for the “Features” tab on the top of the page. On the “Features” page, look for the “Simultaneous Ring” feature under the “Outbound Call Features” and open it. Once you are on the "Simultaneous Ring" page, enable the feature by selecting "N" from the drop-down menu next to the "Enable" tab. Once done, simply add the numbers that you want to ring simultaneously in addition to your VoIP phone (you don't need to add your VoIP number here).
You can add up to three numbers to simultaneously ring with your AXvoice VoIP phone.