This limitation means that I cannot see who is calling if the number is outside my organization and that I cannot directly call someone outside my organization. It's a serious limitation that ought to be fixed right away.
I am able to successfully get my Outlook contacts to show up in RingCentral Phone 10.3.5.34099, after going into the settings under "Contacts" and enabling "View Outlook contacts". You'll also need to pick a contact folder to enable under "Select folder". Overall, this appears to be working fine, and you don't even need the plug-in.
Edit: I just heard that the plan is 2nd quarter of this year.