RingCentral needs to add a very valuable service to its system. A Corporate Directory that can contain external contacts. Microsoft does this with their email servers because it is a valuable feature for communicating with people outside of your own company and managing that information centrally.
For example: Multiple people in my company communicate with someone outside of the company. Microsoft allows you to add an external contact (name, phone, email) so that everyone (or designated people) can benefit from not directly knowing that info but have it appear in an email To, CC, or BCC line by typing their name when creating an email. If that info changes, the admin can update that entry and again, everyone who needs it benefits instantly.
RingCentral needs to have a corporate directory that allows for external contacts so that the information can be centrally maintained and then put onto people's phone screens as a button similar to the Presence feature for internal contacts. This would allow for central management of "common" contacts that are used by folks in the company and by placing them as buttons on the phones, making it easier for people who call those contacts frequently to do so by using the button.