Disclosed herein are methods and systems for enforcing prepayment based on lack of support of authentication functionality by a particular wireless serving system. In one embodiment, at least one home-core-network entity associated with a home core network of a mobile station receives from a particular wireless serving system a registration request associated with the mobile station. Responsive to receiving the registration request, the at least one home-core-network entity makes a determination as to whether the particular wireless serving system supports authentication functionality. Responsive to the determination being that the particular wireless serving system does not support authentication functionality, the at least one home-core-network entity sends to the particular wireless serving system a registration response that grants the request subject to at least one prepayment requirement.