If you phone de-registers from the base, try these steps.
Step 1
Click OK.
Step 2
Click Settings.
Step 3
Click Registration.
Step 4
Click Register Handset.
Step 5
Select Base1.
Step 6
Once you've selected Base1, press the button on the base for 2 seconds to allow the phone to sync with the base.
Step 7
Enter the PIN, 1000