Successfully contacting colleagues while away from the office is especially difficult without information about their availability and location. HandiMessenger is a service designed to facilitate opportunistic communication by tightly integrating awareness and contact capabilities into a wireless, unified messaging and awareness application. Users can securely access intranet email, instant messages, and other messages from a handheld mobile device (e.g., a wireless PDA). Simultaneously, they are presented with awareness information about the sender to enable a reply in the most appropriate mode, given the situation of the participants. For example, they can read email and reply by initiating a phone call, if the sender is available by phone. Analysis of handiMessenger usage shows that users do request awareness information while inspecting message headers or content, and that users also, at times, respond to a message with a different type or in a different mode than the original message.