No Caller Display on some calls

[#1]

Has anyone noticed that some calls do not provide Caller Display details?
I am not talking about "International", "Out of area" or "Unavailable" numbers - in such circumsatnces those words are displayed.  I have seen a couple of calls which only display "Incoming Call" on the phone and do not indicate a number nor for that matter leave a call history on the phone itself.  Phnes are Panasonic DECT.  Cannot know for sure that the call was from a mobile, but  the caller furnished a mobile as the contact number.
Any ideas???

[#2]

If a the caller prefixes the number with 141 the CLI info is withheld

[#3]

DWR,
Interesting... I was about to suggest that you were wrong, as I thought such numbers report "WITHHELD Private Caller" (as shown on a call received 27th Dec 15:14) however on doing a test from my MOBILE phone, I discovered 141 does indeed result in no idenity or evidence of the call being left on the Caller ID phone history.
Either there has been change in the system in the last 24 hours or (possibly) 141 in in front of (possibly just EE / Orange / T-Mobile) numbers produces this result.
Cheers,
Kevin

[#4]

I think it has been around for a long time  - I did a Google to make sure that I was correct.
See
http://btbusiness.custhelp.com/app/answers/detail/a_id/7693/~/141-and-1470

[#5]

Yes, the ability to block the display of your number has indeed been aroud for a very long time, however the called party usually sees "WITHHELD Private Caller".  Just recently though I am not seeing any such message and the phone caller history logs no record of a call whatsoever.
Confused!

[#6]

Probably related to your line fault