<p>With the rapid development of quantum computing, traditional cryptographic schemes such as RSA and ECC are becoming increasingly vulnerable. This raises an urgent need to transition toward post-quantum cryptography (PQC) in Internet of Things (IoT) systems, where many devices have long lifecycles and limited ability to receive software or hardware updates. Narrowband IoT (NB-IoT), a widely adopted low-power wide-area network (LPWAN) technology, is commonly used in smart metering, environmental sensing, and remote monitoring applications. However, NB-IoT devices often operate under strict resource constraints—limited memory and low processing speed—making it challenging to implement complex security protocols, especially PQC algorithms with higher computational costs. This paper presents a comprehensive hybrid secure communication framework that fully integrates three distinct security layers—quantum-safe key exchange, forgery-resistant digital signatures, and efficient data encryption—with lightweight cryptographic primitives, aiming to achieve both quantum resilience and practical compatibility with constrained NB-IoT devices. The proposed solution combines three key components: CRYSTALS-Kyber for quantum-safe key exchange, SPHINCS+ for stateless digital signatures resistant to forgery, and ChaCha20-Poly1305 for efficient data encryption on software-based platforms. We implement and evaluate the system on an ESP32 microcontroller integrated with an NB-IoT module, measuring key performance metrics such as processing time, power consumption, and packet size overhead. Results show that while the initial handshake incurs higher computational overhead compared to classical schemes (e.g. ECC-based TLS), the system remains feasible for real-world deployment through intelligent session management and optimized scheduling strategies. This work contributes a practical, application-oriented solution for building quantum-resilient IoT infrastructures in the near future.</p>