What does gsmAccess() function do (GSM.h and Arduino)

Question

I have a module which connects and sends ussd through arduino+GSM shield. I am kind of fuzzy on the following two commands which are commented with ??. (line 4 and line 7).

Can someone explain what these two do?

And plus gsmAccess.getStatus() == 3; what are the other values that this function can return apart from 3?

#include <GSM.h>
#include <GSM3ShieldV1DirectModemProvider.h>
GSM3ShieldV1DirectModemProvider modemAccess;
GSM gsmAccess(true);                           // ??

void sendCommand(String com){                 // com is "AT+CUSD=1,\"#366#\",\0"
  if(gsmAccess.getStatus() == 3)              // ??
    Serial.println(modemAccess.writeModemCommand(com,comDelay));
  else{
    connectModule();
    sendCommand(com);
  }    
}

Answer 1

The line:

GSM gsmAccess(true);

initializes the GSM library to enable an Arduino to act as though it were a mobile (cell) phone. The true parameter puts the library into debug mode which will print out all the AT commands from the modem (reference).

The line:

if (gsmAccess.getStatus() == 3)

is checking that the GSM library is ready to send commands. The 3 is the code for GSM_READY as defined in the source code

For clarity it would be better to write this line as:

if (gsmAccess.getStatus() == GSM_READY)

The other statuses (defined in the same source file) are:

0: ERROR
1: IDLE
2: CONNECTING
3: GSM_READY
4: GPRS_READY
5: TRANSPARENT_CONNECTED
6: OFF