If the unity client is always prompting for the server address when loading please check the following…

Check the file InstallationSettings.xml located at C:\Program Files (x86)\Unity Client. Right-click on this file and open it in Notepad or a text editor.

Ensure that around line 6 contains the following text: <VoipHostServer>xsi.voicesys.co.uk</VoipHostServer>

If it does not, please add the line as shown above. Save the file and then try loading the Unity Client again.