Area code the caller id does not show the area code of the call coming in

Here is a link to the site containing a pdf manual link and this is an excerpt for you :

Long Distance calls and Area Code Setting/Cancellation
While the present Caller ID information is displayed, pressing */tone/< will place
or remove the prefix "1" in the display to set the call for a long distance call, or
pressing #/> will set or cancel an area code (see page 30).
Storing Caller ID messages in the Phonebook
Messages shown in the Caller ID list can be stored in the phonebook. The phone
number and name of the party on the Caller ID list can be stored in memory.
1) When the phone is in standby mode, select the Caller ID message to be stored.
Then press the STORE soft key on the base or the EDIT soft key on the handset.
From the handset, then select E D I T ?. S t o r e / E d i t N a m e appears. If the Caller ID
message is already stored in memory, you will hear a beep and T h i s d a t a i s
a l r e a d y s t o r e d ! ! appears. The number will not be stored.
2) To complete the setting, follow the steps 3-8 in "Phonebook (Storing Phone
Numbers, Names, Distinctive Rings, and Speed Dial)" on pages 42-43.