The Internet of Things (IoT) enables the connections of billions of devices to the Internet. It is thus very important to effectively manage this huge amount of devices. Among many available device management protocols, Open Mobile Alliance Lightweight M2M (OMA LWM2M) has been adopted by the global M2M standards, ETSI M2M and oneM2M as the standard for device management. However, OMA LWM2M-supported devices are still not widely available because the standard is relatively recently published. On the other hand, there are millions of legacy devices and sensors that do not support the OMA LWM2M protocol. Consequently, how to integrate non-OMA LWM2M devices so that they can be managed by OMA LWM2M Server is urgently needed. Moreover, how to exercise OMA LWM2M device management from the M2M standards is also not well addressed by the standard. In this paper, we address both challenges by first designing an OMA LWM2M gateway between OMA LWM2M server and non-OMA LWM2M devices (legacy devices). Then we further integrate this gateway in the ETSI M2M and oneM2M-like standard architecture. The paper not only explains the capabilities of our system in detail but also analyzes the differences between the OMA system standalone and the one embedded in the M2M standard architecture.