There are 2 ways to get out of PTT mode:
Get another device & connect them together, then go to My Documents & under the menu options there's one that lets you exit this mode.
If you don't have another device or that cable, then you can connect it to the computer & send a file named "Exit Test Mode" (is CASE sensitive, so beware of that), which you must send inside the "Press-to-Test" folder