Hello,
I recommend you to try domo application WirelessUART from BeeStack codebase. Using this application, you can send character between two boards, in each sense (from coordinator to end device and from end device to coordinator). Also, for more informations, please read Freescale ZigBee™ Application User’s Guide (ZAUG.pdf), Chapter 5 Creating a Wireless UART application.
Regards,
Adrian