HTTP Post Analog Value With GSMSim Library. First add GSMSim Library to Arduino with using Library Manager.

GSMSim_HTTP_Post_Analog_Value.ino

/*
 * GSMSimHTTP Post analog value Example
 * 
 * GSMSim_HTTP.ino
 *
 * By Erdem ARSLAN
 * Version: v.2.0.1
 *
 * The MIT License (MIT)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
*/


/*
  ### Example Serial Output ###

  Set Phone Function... 1
  is Module Registered to Network?... 1
  Signal Quality... 14
  Operator Name... Turk Telekom
  Connect GPRS... 1
  Get IP Address... xxx.xxx.xxx.xxx
  Get... METHOD:GET|HTTPCODE:200|LENGTH:30
  Get with SSL and read returned data... METHOD:GET|HTTPCODE:200|LENGTH:30|DATA:This test data return from GET
  Post... METHOD:POST|HTTPCODE:200|LENGTH:54
  Post with SSL and read returned data... METHOD:POST|HTTPCODE:200|LENGTH:54|DATA:This test data return from POST.<br>Hello Erdem Arslan
  Close GPRS... 1

*/

#include <GSMSimHTTP.h>
#include <SoftwareSerial.h>

// You can use any Serial interface. I recommended HardwareSerial. Please use the library with highiest baudrate.
// In examples, i used HardwareSerial. You can change it anymore.

#define RESET_PIN 10 // you can use any pin.

#define analogPin = A0;

SoftwareSerial gsmSerial(7,8);

GSMSimHTTP http(gsmSerial, RESET_PIN); // GSMSimHTTP inherit from GSMSimGPRS. You can use GSMSim and GSMSimGPRS methods with it.

void setup() {
  gsmSerial.begin(57600); // If you dont change module baudrate, it comes with auto baudrate. 

  while(!gsmSerial) {
    ; // wait for module for connect.
  }

  Serial.begin(115200); // Serial for debug...

  // Init module...
  http.init(); // use for init module. Use it if you dont have any valid reason.

  Serial.print("Set Phone Function... ");
  Serial.println(http.setPhoneFunc(1));
  //delay(1000);

  Serial.print("is Module Registered to Network?... ");
  Serial.println(http.isRegistered());
  //delay(1000);

  Serial.print("Signal Quality... ");
  Serial.println(http.signalQuality());
  //delay(1000);

  Serial.print("Operator Name... ");
  Serial.println(http.operatorNameFromSim());
  //delay(1000);


  //Serial.print("GPRS Init... ");
  //Serial.println(http.gprsInit("internet")); // Its optional. You can set apn, user and password with this method. Default APN: "internet" Default USER: "" Default PWD: ""
  //delay(1000);

}

bool postData(int analogValue) {

  bool isPostOK = true;
  
  Serial.print("Connect GPRS... ");
  isPostOK = http.connect();

  if (isPostOK) {
    Serial.print("Post... ");
    String postAnswer = http.post("localhost/index.php", "params=" + String(analogValue), "application/x-www-form-urlencoded");
    if(postAnswer.indexOf("HTTPCODE:200") != -1) {
      isPost = true;

      Serial.print("Close GPRS... ");
      Serial.println(http.closeConn());
    } else {
      isPost = false;
    }
  }

  return isPostOK;
}

void loop() {

  int analogValue = analogRead(analogPin);

  if(postData(analogValue)) {
    Serial.print("Analog value posted to Server");
  } else {
    Serial.print("Analog value NOT posted to Server.");
  }

  delay(60000); // wait 1 minute
}

index.php

<?php
$timestamp = date("d-m-Y - H:i:s");
$datastring = $_POST["params"];
$myfile = fopen("newfile.txt", "w") or die("Unable to open file!");
$txt = $timestamp . " - ".$datastring."\n";
fwrite($myfile, $txt);
fclose($myfile);
echo $txt;