Machine-to-machine (M2M) communication between devices has significant differences with conventional human-to-human (H2H) communications. From these differences, considerable technical issues of M2M communication arise, which are expected to result in numerous system changes compared to existing H2H communication networks. M2M-based features offer a new paradigm for future communication and network services, and can enable various convergence services in support of ubiquitous businesses and complex manufacturing industries. However, currently one limiting factor is lack of end-to-end M2M network connectivity. Various global standardization groups are conducting standardization on M2M communications. In this paper, a summary on the progress of global M2M standardization is presented. This paper also introduces M2M technical issues and discuss on the necessity of M2M vertical handover (VHO) and technical requirements in support of M2M VHO and fast handover for proxy mobile IPv6 (FPMIPv6) VHO between heterogeneous M2M protocol networks to enable end-to-end M2M network connectivity.