In this case, the call data has to be transmitted from the Internet to the landline network, usually using what are known as VoIP gateways. In general, these gateways are provided by providers and are subject to a fee.
VoIP routers offer another option that can switch VoIP calls to an ISDN line. Examples are different LANCOM VoIP Router types with an SIP gateway and ISDN interfaces. When the calls are transferred to the landline network, the usual telephone operator fees are charged.
So that the subscriber can even be called on a PC, he or she needs a VoIP telephone number that is usually provided by a provider.
VoIP providers usually only provide individual numbers and not complete number ranges with a switchboard number and extension numbers. This is why the numbers that are provided by public providers are not attractive to many business customers. When the LANCOM VoIP Router is used with a SIP gateway, previously-used numbers can be maintained; the functions of VoIP telephony can also be used.