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[+44 330 383 8000](tel:+443303838000 "+44 330 383 8000") ![](/images/getstarted-writetous-navbar-int_ZY7MOf.webp) ### Write to us Fill out our request form. Our experts will respond as soon as possible. [Write to us](/gb/request-information "Write to us") ### Completion of Calls to Busy Subscriber (CCBS) # Completion of Calls to Busy Subscriber (CCBS) The abbreviation CCBS is for the technical term "Completion of Calls to Busy Subscriber", a [telephone system](/gb/gb/products/cloudya) feature. It can be used when a call is made, but the busy tone for the called party is heard. In this event, CCBS can be activated by performing certain actions and the caller will be called back by the telephone system as soon as the desired subscriber ends their current call. If the caller takes this new call from the system a new connection is initiated to the originally called party. If the line is still free, they can take the call and the connection is made. The great advantage of the CCBS service feature is that the caller does not need to repeatedly make multiple calls to try to reach the called party, but as soon as their line becomes free again this is signalled directly by the telephone system. This saves time and allows the caller to continue working in the meantime. CCBS is a feature that can only be used internally within a system. It can be provided for the entire system or only for individual participants. Call-back requests are easily activated using a short code. Not to be confused with CCBS, an automatic redialling feature, which is activated in the phone device itself. It is used when a caller gets an engaged signal and their phone then calls the recipient at a user-defined time interval until the line becomes free again. ### Related Articles ### Callback Callback is a special method that can be used in telephony, whereby return calls can be requested from a service [provider](/gb/get-started/cloud-telephony/lexicon/knowledge-base-detail/telephone-provider). The actual connection is established by a service provider that does the calling back. This makes it possible to conduct calls via a different telephone provider from the one that provides your telephone line or mobile telephone, and be billed by the third party service provider. This method is often used to optimise phone charges or to give employees the opportunity to make calls via their own work phone connection, without the company incurring the costs of private telephone calls. It can also be used when a company's phone line does not support Call-by-Call, to allow them to select another phone service provider to make calls through. 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