Getting Unavailable when checking the contacts list can be because the Base Station is disconnected from the Line or Ethernet connection or another user may be using the contact list or Skype menu 

To resolve this, follow the instructions below. 

Step 1:
Check the connection between the Base Station and the telephone line or the network Ethernet cable. 

Or

Step 2:
Make sure the Handset and the Base Station are connected. Press the PAGE button on the Base Station to check if it is connected to the Handset. The Handset will ring to acknowledge the page. 

Step 3:
The contacts list will be inaccessible if another user is using the contact list or Skype menu. Try accessing the contact list later.