Abstract: A wide-area network (“WAN”)-based service enables remote data access transactions between participating endpoints within a group of participating endpoints that includes at least one server and at least one portable electronic device. Each participating endpoint is configured for communication via one or more communication networks and stores the same or different data items on behalf of a user. The WAN-based service maintains information about each participating endpoint in the group and its network accessibility, and also maintains one or more catalogs of available data items. The WAN-based service identifies a communication network available to both participating endpoints, and a direct or proxied communication session is established between the portable electronic device and the other participating endpoint via the communication network. Selected data items are downloaded, uploaded, accessed or synchronized via the communication session.