Methods, systems, and computer readable media for seamless roaming between networks are disclosed. According to one aspect, the subject matter described herein includes a method for seamless roaming between networks. The method occurs at a home subscriber server (HSS). The method includes maintaining registration status information for a subscriber. The method also includes communicating with a first network via a first network interface and with a second network via a second network interface using the registration status information to facilitate roaming between the first network and the second network. The first network interface is configured to receive and send Diameter signaling messages for managing mobility of the subscriber and the second network interface is configured to receive and send non-Diameter signaling messages for managing mobility of the subscriber.