From the manual:
About Emergency Callback Mode
When you end an emergency call, the BlackBerry� device enters Emergency Callback Mode. This mode enables the operator to call you
back or determine your approximate location. Depending on your service provider, Emergency Callback Mode is active for five minutes or
is canceled when you make a non-emergency call.
In Emergency Callback Mode, you cannot send and receive messages or browse web pages.
Your device exits Emergency Callback Mode at any time if you make a non-emergency call.