As I don't want to stack the shield over the mega 2560 board, I try to connect only the pins that used for GSM communication. Here are my connection:

Pin 3 on Mega <==> Pin GSM Rx on Shield

Pin 10 on Mega <==> Pin GSM Tx on Shield

Pin 4 on Mega <==> Pin 4 on Shield

Pin 5V on Mega <==> Pin Vin on Shield

Pin GRD on Mega <==> Pin GRD on Shield

Code I used is from the Examples library, GsmScanNetworks:

#include <GSM.h> // PIN Number #define PINNUMBER "8888" // initialize the library instance GSM gsmAccess; // include a 'true' parameter to enable debugging GSMScanner scannerNetworks; GSMModem modemTest; // Save data variables String IMEI = ""; // serial monitor result messages String errortext = "ERROR"; void setup() { // initialize serial communications and wait for port to open: Serial.begin(9600); while (!Serial) { ; // wait for serial port to connect. Needed for Leonardo only } Serial.println("GSM networks scanner"); scannerNetworks.begin(); // connection state boolean notConnected = true; // Start GSM shield // If your SIM has PIN, pass it as a parameter of begin() in quotes while(notConnected) { if(gsmAccess.begin(PINNUMBER)==GSM_READY) notConnected = false; else { Serial.println("Not connected"); delay(1000); } } // get modem parameters // IMEI, modem unique identifier Serial.print("Modem IMEI: "); IMEI = modemTest.getIMEI(); IMEI.replace("\n",""); if(IMEI != NULL) Serial.println(IMEI); } void loop() { // scan for existing networks, displays a list of networks Serial.println("Scanning available networks. May take some seconds."); Serial.println(scannerNetworks.readNetworks()); // currently connected carrier Serial.print("Current carrier: "); Serial.println(scannerNetworks.getCurrentCarrier()); // returns strength and ber // signal strength in 0-31 scale. 31 means power > 51dBm // BER is the Bit Error Rate. 0-7 scale. 99=not detectable Serial.print("Signal Strength: "); Serial.print(scannerNetworks.getSignalStrength()); Serial.println(" [0-31]"); } 

Questions:

1. After opening the serial port, only a line "GSM network scanner" is read. Seems that the program is stuck ongsmAccess.begin(PINNUMBER), how shall I fix that?
2. Is it a must that I shall supply 5V 2A power to the shield seperately in order for the shield to work? (with connection mentioned above, the ON led light on the shield does turns on with an orange light)
3. For the PINNUMBER defined in the program, my SIM has default PIN 8888. I checked with a mobile phone that the SIM card does work. But my phone shows that the SIM card is not locked with PIN. So shall I define the PIN as 8888 for ''?