A wireless phone user registered for push-to-talk (PTT) services desires a push-to-talk session with a party on a network computer accessible via a public data network (like the Internet) that is not registered with any PTT service. The registered user enters a unique identifier, as a destination address for such computer, and a PTT server uses the unique identifier to query a Directory Service available on the public data network to obtain a PTT address for the destination computer. The PTT server then forwards or proxies the PTT request to the destination computer. As a result, the number of push-to-talk destinations available to the wireless phone user is expanded to include any number of push-to-talk enabled computers available on the Internet that are known to the Directory Service.