On any version of Android, dating back to the introduction of the virtual keyboard in version 1.6, long-pressing on the menu button will pop up the keyboard, which allows you to, for instance, bring up the keyboard in applications without needing a specific textbox to select. This allows you to have applications like ConnectBot, where the entire screen is a terminal emulator, and you can pop up the keyboard at any point and start typing without having to type into a textbox and then "send" the text to the terminal. On the home screen, you can bring up the keyboard and just start typing a search query without needing to press (or even have) the search button or widget.
And for the record, when the virtual keyboard is shown, pressing the back button will always dismiss it without sending the back action to the current activity, so in your case you could have pressed back to dismiss the keyboard, and then pressed the button to receive the call.
