I dont have the bluetooth, but I think its because the incoming number must match the number in the caller ID exactly.
Lets say for example that the number shows up at 123-456-7890, but it is in your contacts under 'John' as '456-7890', it will not show the number.
If you have the number as 123-456-7890, it should display John when you receive a call.
You can always test this by changing the entry for 'Home' to include the area code. Call your cell from your house and see if it displays properly.