Your ISDN device will continue to work with IP. With the Swisscom Line basic telephony package and the option for 2 additional phone numbers, you will receive a special router with an ISDN interface. This will enable you to keep your existing telephone. However, Swisscom advises against the use of ISDN telephones in combination with the new IP fixed network telephony since customers cannot benefit from all the advantages of IP telephony, such as HD Voice. Swisscom cannot guarantee that additional device-specific ISDN features and non-telephony ISDN devices, such as alarm systems, will work properly.