(Dialed Number Identification Service). DNIS is a feature of 800 and 900 lines that provides the number the caller dialed to the receiving switch. Using DNIS capabilities, one trunk group can be used to serve multiple applications. The DNIS number can be provided in a number of ways, in-band or out-of-band, ISDN or via a separate data channel. Generally, a DNIS number will be used to identify to the answering telephone system the application the caller dialed.