Problem with GSM Shield

With all the code uncommented out, how much free memory do you have?
http://playground.arduino.cc/Code/AvailableMemory

There are a lot of string literals that are copied, unnecessarily, into SRAM at run time. Stop that from happening by wrapping them in the F() macro:
Serial.println(F("DHT11 Starting... "));

String url = "";

Quit pissing away resources on the String class. Be a big boy (or girl) and learn to use C strings (NULL terminated arrays of chars).