I get this compiling error with your lib? Do I need additional libs?
In file included from GPRSTest.ino:8:
C:\Program Files\Arduino\libraries\SIM800/SIM800.h: In member function 'bool CGPRS_SIM800::available()':
C:\Program Files\Arduino\libraries\SIM800/SIM800.h:79: error: 'Serial1' was not declared in this scope
EDIT:
Found this thread: Sleep and wake up with DS3231 - Networking, Protocols, and Devices - Arduino Forum