A VoIP-based telephone system can be affected by faulty configurations in the same manner as a circuit-switching telephone solution. Telephone users could be assigned incorrect telephone numbers, for example, or the entire telephone infrastructure could fail. Even minor errors, such as a name spelled incorrectly in the telephone book, cannot be ruled out.

When VoIP is used for communication, several IT systems are usually involved. If SIP is used as the initialisation protocol, systems such as registrars, SIP proxy servers, and location servers are usually required for communication. If the VoIP infrastructure at hand changes, all the related IT systems must be adapted. This can easily lead to configuration errors. Even when all services are located on one server, they often need to be configured individually. An incorrect change made to just one system could render the entire telephone infrastructure unusable.