Your Crystal is 4 MHz. So, you want to use AVR microcontroller. You images are not helpful. Build your circuit first ie., connect LCD, Keypad, etc... to the required PORT(s) and post the circuit diagram. Then only Code can be written. Use Proteus from labcenter.co.uk to draw the Schematic. In trial version you cannot save the file but you can take the screenshot of the circuit.
If your PC has serial port (RS232) then connect your SIM300 board to it and issue GSM Commands and check if is working. Try to send SMS. If your PC doesn't have RS232 then use Serial to USB Converter and connect your SIM300 board to USB port of PC and test it.
What AVR you want to use?