gistfile1.txt

Code change in Modem.cpp:
----------------------------------------------------
void ModemClass::poll()
{
  while (_uart->available()) {
    char c = _uart->read();

    if (_debugPrint) {
      _debugPrint->write(c);
	    Serial.print("["+(String)(_uart->available())+"]");   // Prints buffer size to SM after each char is read
    }

    _buffer += c;
    
----------------------------------------------------

Serial monitor output with this extra code:

10:05:19.844 -> [0]A[26]T[25]+[24]C[23]M[22]G[21]L[20]=[19]"[18]R[17]E[16]C[15] [14]U[13]N[12]R[11]E[10]A[9]D[8]"[7]
[6]
[5]
10:05:20.950 -> [4]O[3]K[2]
[1]
10:05:20.950 -> [0]A[63]T[62]+[61]C[60]M[59]G[58]L[57]=[56]"[55]R[54]E[53]C[52] [51]U[50]N[49]R[48]E[47]A[46]D[45]"[44]
[43]
[42]
10:05:22.053 -> [41]+[40]C[39]M[38]G[37]L[36]:[35] [34]1[33]5[32],[31]"[30]R[29]E[28]C[27] [26]U[25]N[24]R[23]E[22]A[21]D[20]"[19],[18]"[17]+[16]1[15]#[14]#[13]#[12]#[11]#[10]#[9]#[8]#[7]#[6]#[5]"[4],[3],[2]"[1]2[0]