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A number can be withheld during digital, analogue or [voice-over-IP (VoIP)](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/voice-over-ip) telephone calls. The process of withholding a number is also called Calling Line Identification Restriction (CLIR). The recipient of a withheld number call usually sees a message such as “unknown” or “withheld number” in their phone display instead of a [phone number](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/national-international-phone-numbers). ### CLIR ![](https://a.storyblok.com/f/290788/64a537abb4/clir.jpg) ### How can I withhold my phone number when I call someone? Normally, you can activate CLIR for individual calls, or you can install the functionality permanently. For example, landline customers can prefix their dialed number with special digits to make their number unrecognizable to the recipient. The number sequence required for this differs from provider to provider. ### Does CLIR anonymize my phone calls? CLIR allows callers to remain anonymous to a certain extent. However, it is important to mention that CLIR only causes the phone number not to be visible to the recipient. The phone system or the phone provider can recognize your phone number and identify you. ### Is my number always hidden? In most cases. However, there are exceptions, for example in the case of emergency call centers. The fire department, police or emergency services always see the caller's number - even in cases where CLIR is activated. This ensures that help can be provided at any time and as quickly as possible as soon as you dial 911. Another reason is to protect against misuse of such emergency numbers. In addition, there are some legal requirements that say that certain people are excluded from CLIR, for example when it comes to telephone solicitation. ### Can I use CLIR with VoIP? In the case of the [NFON Cloud Telephone System](/gb/en/products/cloudya), VoIP users can benefit from all the advantages and functionalities that traditional telephony has to offer. This includes call number withholding according to your personal preferences. ### Related Articles ### Voice over Internet Protocol (VoIP) **What is VoIP?** The **Voice over Internet Protocol,** also called IP telephony, is a method of communication for making calls over a broadband Internet connection as an alternative to regular calls made over an analogue phone using the [PSTN](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/pstn). These VoIP calls can happen entirely over the Internet but where required, gateways also link to the PSTN. This means that VoIP users can still connect to anyone with a telephone number including local, mobile, and international numbers. VoIP services can be accessed from a computer with a so-called [softphone,](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/softphones) from an IP phone, from a smartphone or from a conventional landline phone that is connected to a VoIP adapter. 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