Make sure you have the latest version of Pocket Tunes, 3.1.8 or higher (available here if you do not have it).

With that version we added support for the T|X Keylock. However please note that it you use the Manual Keylock function, holding the power button down for 2 seconds will cause the Palm operating system to turn Pocket Tunes off as well. Instead, simply press and release the power button and the keys will be locked until you press the power button again to turn the screen back on.

NOTE: Ensure that BOTH "Turn off screen after xx seconds" and "Power buttons turns off screen" are activated in the General Preferences screen.