Google Scripts code for sending SMS from Google Sheets – from https://medium.com/46-thoughts/send-sms-from-google-spreadsheet-71f11d358361

Code.gs

function elksSMS() {
  // Get the properties 
  var prop = PropertiesService.getScriptProperties();
  var username = prop.getProperty('46elksUsername');
  var password = prop.getProperty('46elksPassword');
  var spreadsheetID = prop.getProperty('SpreadsheetID');
  var sender = prop.getProperty('46elksAccountPhoneNumber');
  var auth = Utilities.base64Encode(username + ":" + password);
  
  // Open the requested SpreadSheet and Sheet
  var spreadSheet = SpreadsheetApp.openById(spreadsheetID);
  var sheet = spreadSheet.getSheets()[0];
  var range = sheet.getRange(2, 1, sheet.getLastRow() - 1, 5).getValues();
  
  // Loop over all rows in the range and send the SMS
  for (var i in range) {
    if (range[i][1] == '' || range[i][3] == 'SENT') continue;
    var state = sheet.getRange(2+Number(i), 4);
    var info = sheet.getRange(2+Number(i), 5);
    try {
      UrlFetchApp.fetch("https://api.46elks.com/a1/SMS", {
        "method": "post",
        "headers": { "Authorization": "Basic " + auth },
        "payload": {
          "from" : sender,
          "to" : '+' + range[i][1],
          "message" : range[i][2]
        }
      });
      state.setValue('SENT').setBackground('#93c47d');
      info.setValue('Sent on ' + new Date());
    } catch (err) {
      state.setValue('FAILED').setBackground('#e06666');
      info.setValue(String(err).replace('\n', ''));
    }
  }
}