GSM SIM900A SMS content not displaying
Your code is absolutely correct. As I tested it with my Mega with Serial3 connected to GSM SIM900. I think there is something fishy about SoftwareSerial. Double-check the location of SoftwareSerial.


  C:\Program Files (x86)\Arduino\hardware\arduino\avr\libraries\SoftwareSerial\src


Maybe you can see if RAM usage is exceeding the safe limit. Here is my output: