A method of allowing a network communication service user (subscriber) to receive a desired network communication service with a constant (the same) quality regardless of being in a wired or wireless communication environment based on a single service level agreement (SLA) of the subscriber is provided. The method of providing the network communication service with the constant quality regardless of the wired or wireless network environment includes: (a) setting a call control policy for a service so that an SLA (service level agreement) of a network communication service user is available for the wired or wireless network; (b) determining whether the user accesses the network through the wired or wireless network; (c) determining whether the user is a wired network home user or a wired network guest user when the user accesses the network through the wired network; and (d) providing a network communication service requested by the user based on the call control policy based on the determination result of (b) and (c) for the user.