Communication technology has been seeing rapid growth, characterized by new access networks (e.g. cellular, pager, wireless-IP) and end-devices (e.g. PDAs, two-way pagers, multi-model access devices). There have been several efforts at integrating services across such heterogeneity. However, little work has been done on identifying an underlying architecture for such an integration. We identify the requirements for this in the context of an integrated network with heterogeneous end-points. The Universal Inbox provides (a) generic data type transformation, (b) customizable redirection of incoming communication based on user preference profiles, and (c) device name mapping and translation. We present an architecture mapping these functionalities to reusable infrastructure components realized as Internet services. The unique feature of the architecture is its extensibility-it allows not only the integration of existing end-points but also extension in terms of the end-devices and novel services it can handle. We have implemented the Universal Inbox components in a test-bed setting, supporting a variety of devices and services: GSM cellular phones, voice-over-IP end-points, voice-mail, e-mail, instant messaging service, etc. With our architecture, building personal mobility and service mobility features and extending them to new end-points has been easy in concept and in implementation. The performance analyses with the initial implementation show that even the heavy-weight components can be scaled to accommodate a large user base.