Share your ideas with us
On an existing extension, selecting Add Phone under Phones & Numbers> Phones the screen shows the annual charge if you already have licenses and inventory available. There should be more information on this page about how many licenses you currently have available, and what will be used during this "transaction" -or- at the final step, show a $0 additional charge.
David, I have spoken with the product team and they have confirmed this feature has been implemented. If you have further requirements you don't feel have been addressed, please reach out to us at Ideas@RingCentral.com