Editing Caller ID (section)

==Blocking and unblocking caller ID==
{{anchor|Blocking}} <!-- [[Automatic number identification]] links to this anchor, and [[Caller ID blocking]] redirects here. -->
[[File:Skype-Call.png|thumb|upright=0.6|The caller ID information is masked when a [[Skype]]Out call is placed.]]

'''Caller ID blocking''' is the common term for a service by which a caller can prevent the display of the calling number on the recipient's telephone. Blocking the number is formally referred to as ''calling line identification restriction'' (CLIR). This customer option was part of the legal authorization for New York State's 1992 authorization of Caller ID.<ref name=OKonID1992NYT>{{cite news
   |newspaper=[[The New York Times]]
   |url=https://www.nytimes.com/1992/03/12/business/new-york-state-approves-caller-identification-service.html
   |title=New York State Approves Caller-Identification Service
   |author=Anthony Ramirez
   |date=March 12, 1992
   |access-date=September 21, 2022
   |archive-date=September 22, 2022
   |archive-url=https://web.archive.org/web/20220922040912/https://www.nytimes.com/1992/03/12/business/new-york-state-approves-caller-identification-service.html
   |url-status=live
   }}</ref>

Telecommunications regulators vary in their requirements for the use and effectiveness of assorted technologies to prevent numbers from being displayed.  Generally, [[unlisted number]]s are always blocked. Non-published and regular listed numbers are not usually blocked.  But there is varying treatment for the determination of call display blocking because of many factors.  If desired, customers should inquire carefully to make sure their number will not be displayed.  The telephone service provider may also have vertical service codes which can be dialed to configure blocking as active for all calls or on a call-by-call basis. In some locations{{where|date=May 2023}} in the United States, regulations allow (or require) blocking to be automatic and transparent to the caller.

Where blocking is applied on a call-by-call basis (that is, at the time a call is made), subscribers can block their caller ID by [[Dial (of telephone)|dial]]ing a special code (a vertical service code, or VSC) before making a call. In [[NANP|North America]] and some other regions,{{which|date=May 2023}} the code is *67 (1167 on [[Rotary dial|rotary phones]]), while in the [[United Kingdom]] and [[Ireland]], it is 141.  This special code does not block the information from companies using call capture technology. This means that equipment with caller ID will simply display the word "PRIVATE" or "WITHHELD".  When CNID is blocked at the caller's request, the number is actually transmitted through the entire telephone network, with the "presentation withheld" flag set; the destination CO is expected to honor this flag, but sometimes does not{{snd}}especially when the destination phone number is served by an ISDN [[primary rate interface|PRI]].  <!-- does PRI even matter?  Would it not be transmitted on BRI too? -->

Alternatively, in cases where caller ID is being blocked automatically, it can only be released on a call-by-call basis by dialing a special code (*82 in North America; 1470 in the UK). See "Enabling", below.

Similarly, some countries{{where|date=May 2023}} offer [[Anonymity|anonymous]] caller rejection, which rejects all calls when the subscriber's name, number (or both) is blocked.  Some [[telephone company|telephone companies]] protect their clients from receiving calls with blocked information by routing anonymous calls to a service (such as AT&T Privacy Manager), where the caller is required to announce themself.  The service then asks the called party if they want to accept or reject the call.  Other telephone companies play a recording to the caller advising them of the called party's rejection configuration, and often offer advice (such as prefixing their dialing with *82) on how to get their call to the intended called party. [[Emergency service]]s will most likely be able to show the restricted number using a service called ''calling line identification restriction override'' (CLIRO), or by using general ANI services. These features create a [[cat-and-mouse game]] situation,<ref name=CatMou>([[Wired (magazine)|Wired]]){{citation
   |url=https://gizmodo.com/trapcall-displays-blocked-numbers-on-your-caller-id-5155206
   |title=TrapCall Displays Blocked Numbers on Your Caller ID
   |author=Sean Fallon
   |date=February 17, 2009
   |access-date=September 21, 2022
   |archive-date=September 22, 2022
   |archive-url=https://web.archive.org/web/20220922051754/https://gizmodo.com/trapcall-displays-blocked-numbers-on-your-caller-id-5155206
   |url-status=live
   }}</ref> whereby subscribers must purchase additional services in order to cancel out other services.

===Disabling caller ID delivery===
Depending on the operator and country, there are a number of prefix codes that can block or disable Caller ID transmission by the caller. Prefixing a telephone number with the following codes disables Caller ID on a per-call basis:

{| class="wikitable"
|-
!Country !! Prefix
|-
|Albania || #31# (cell phones)
|-
|Argentina || *31# (landlines) or #31# (most cell phone companies)
|-
|Australia || #31# (mobile phones)<ref>{{cite web |url=http://exchange.telstra.com.au/2012/06/19/how-to-block-your-number-when-calling-someone/ |title=HOW TO: block your number when calling someone |date=19 June 2012 |access-date=February 19, 2019 |first=Leigh |last=Price |website=Telstra Corporate Affairs |archive-date=4 March 2017 |archive-url=https://web.archive.org/web/20170304074547/https://exchange.telstra.com.au/2012/06/19/how-to-block-your-number-when-calling-someone/ |url-status=dead }}</ref> 1831 (analogue landline) *67 (NBN landline)
|-
|Brazil || #31# (mobile phones)
|-
|Bulgaria || #31# (mobile phones)
|-
|Canada || #31# (mobile phones) or *67 (landlines)
|-
|Croatia || #31#
|-
|Denmark || #31#
|-
|France || #31# (cell phones) or 3651 (landlines)
|-
|Germany || On most landlines and mobiles, *31#; however, some mobile providers use #31#.
|-
|Greece || *31* (landlines),  #31# (cell phones).
|-
|Hong Kong || 133
|-
|Iceland || *31*
|-
|India || #31# after network unlocked
|-
|Ireland || #31# (dialling from mobile) 141 (dialling from landlines)
|-
|Israel || *43  (landlines) or #31# (most cell phone companies)
|-
|Italy || *67# (landlines) or #31# (most cell phone companies)
|-
|Japan || 184
|-
|Nepal || *9# (NTC)
|-
|Netherlands || *31*, #31# (KPN)
|-
|New Zealand || 0197 (Telecom/Spark), *67 (Vodafone), #31# (2degrees)
|-
|North America || *67, 1167 (rotary phone), #31# (AT&T Wireless)
|-
|Pakistan || *32# PTCL
|-
|Poland || #31# (mobile phones)
|-
|Romania || #31#
|-
|Serbia || *31* (landlines),  #31# (cell phones).
|-
|South Africa || *31* (Telkom)
|-
|South Africa || #31# (Cell Phones)
|-
|South Korea || *23 or *23# (most cell phone companies)
|-
|Spain || #31# (Cell Phones); 067 (landlines)
|-
|Sweden || #31#
|-
|Switzerland || *31# (or *31+Targetnumber -> Call-by-Call disable) (landline)<br/>#31# (or #31+Targetnumber -> Call-by-Call disable) (mobile)
|-
|United Kingdom || 141
|-
|United States || *67
|}

Other countries and networks vary; however, on [[GSM]] mobile networks, callers may dial #31#<ref name="gsmfeatures">{{cite web|url=http://www.arcx.com/sites/GsmFeatures.htm|title=PCS Sites Redirect|website=www.arcx.com|access-date=2008-02-12|archive-url=https://web.archive.org/web/20080203034744/http://www.arcx.com/sites/GsmFeatures.htm|archive-date=2008-02-03|url-status=dead}}</ref> before the number they wish to call to disable it.

Some countries and network providers do not allow Caller ID blocking based on the domestic telecommunications regulations, or CLIR is only available as an external app or value-added service.<ref>{{cite web |url=https://www.lifewire.com/top-call-blocking-app-for-smartphones-4050085 |title=The Best Call Blocker Apps For Smartphones |first=Nadeem |last=Unuth |website=Lifewire |date=December 20, 2018 |access-date=February 18, 2019 |archive-date=February 28, 2019 |archive-url=https://web.archive.org/web/20190228192145/https://www.lifewire.com/top-call-blocking-app-for-smartphones-4050085 |url-status=live }}</ref>

===Enabling caller ID delivery===
Depending on the operator and country, there are a number of prefix codes that can unblock or enable Caller ID transmission by the caller.

{| class=wikitable
|-
!Country
!Prefix code
|-
|Australia || *31# (mobile phones) 1832 (analogue landline) *65 (NBN landline)
|-
|Czech Republic || *31* (landline)
|-
|Denmark || *31*
|-
|Germany || *31# (Some mobile providers)
|-
|India || *31#
|-
|Ireland || *31# (dialling from mobile)<br/> 142 (dialling from landlines)
|-
|Japan || 186
|-
|Hong Kong || 1357
|-
|New Zealand || 0196 (Telecom/Spark)
|-
|North America || *82 (*UB, '''U'''n'''B'''lock)<br/> 1182 (rotary phone).
|-
|Switzerland || #31#
|-
|United Kingdom || 1470
|}

On GSM mobile networks, callers may dial *31#<ref name="gsmfeatures" /> to enable caller ID on all subsequent calls.