A network access system providing network access to a mobile terminal or other device via an untrusted access point such as a wireless access point in an untrusted network. The access point registers with a service gateway, and the wireless terminal connects with the access point and receives a first network address for use with the service gateway. The terminal registers with the service gateway via the access point, and a context identity is maintained at the service gateway, associating the terminal with the access point for the duration of the connection. The terminal can then access a wider network through the service gateway. The service gateway may maintain billing and reward data associated with the context identity.