Can my users pay for the voice server? If so, how?
*Sites created on or after February 1st, 2016 are now able to donate days to voice servers. Learn how to add days to your site and voice server here.
There is not currently functionality in place to directly allow your users to contribute to your billing account. However, if you configure a PayPal Donation widget on your site, they can contribute to a PayPal account which can then be used to pay individual invoices.