Using a file to send multiple contacts Text via GSM sim

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Using a sim800c v3 and a Raspberry Pi4 and AT Commands I have been successful at operating the GSM modem.. But Now I would like to send my company contact list (115) a text at one time ... It would be great to use a CSV/TXT/EXCEL file to do this .. Right now my python code is novice as it gets , But it works ... The question is how do I import file and send to Serial for successful transmission ?


This is my python which works for one text at at time to one number ... looking for Mass SMS or Multiple Contacts

import RPi.GPIO as GPIO
import serial 
import time,sys  

SERIAL_PORT = "/dev/ttyUSB0"
ser = serial.Serial (SERIAL_PORT,baudrate = 9600,timeout=5)

ser.write("AT+CMGF=1\r")
print("Text Mode Enabled....")
time.sleep(3)
ser.write('AT+CMGS="41######"\r')
msg="Yes I know , another TEXT about Team meetup, text back availability"
print("Sending Message ...")
time.sleep(3)
ser.write(msg+chr(26))
time.sleep(3)
print("message sent...")