Our org has a site license for radmin and our phone book is in the hundreds right now.
What I would like to see is an external phone book editor that makes it simple and quick to add and edit entries AND allows us to have different phone books.
Since changing the phone book is simply done by importing the registry key, all one would have to is import the phone book of their choice to switch back and forth between books. That way we can organize our sites in a logical manner.
Also, it doesn't seem that there are any "security" related issues in the phone book. Why not simply publish your registry Hex Format and allow one of us third party folks to come up with an editor to suit our needs and distribute amongst the users.
I think the 3.0 Beta viewer is what you are looking for. It supports saving and loading phonebooks, and it supports organizing things into folders, so you really only need 1 phonebook. We use the 3.0 Beta viewer with 70+ computers, and I would not want to go back to the 2.x viewer. I keep the 3.0 phonebook up to date in my viewer then export it to the LAN for the other IT people to load into their viewers.
Additionally, the 3.0 Beta viewer has a button you can click to see which computers are currently responding, which is extremely helpful.
When you install the 3.0 viewer, it will import your 2.x entries from the registry, so you don't have to start from scratch.