"can some users not be allowed to enter a phone book entry under the all users profile? Is there some type of permission in windows to prevent and would it be safer to add entries under the local profile."
Depending on the version(s) of Windows your application is targetting some do require elevated privileges to access the all users' profile phone book. Not really sure what you mean by "safer", but if you're asking whether the user won't need elevated
rights in the application to access the phone book if it's stored in their profile, the answer is yes. Unless of course the permissions on the file in their profile folder has been changed so that they can't access it, but under normal circumstances they can.
"some ISP's will block VPN traffic, does anyone have a test they could guide me with for checking to see if pptp traffic is blocked."
If they're blocking PPTP traffic, you can probably use telnet to see if you can connect to the remote computer over port 1723, that's the port used by PPTP. Other than that, you can always try to create the connection manually and test if it works.
Hope that helps.