nodemcu-firmware/lua_examples/make_phone_call.lua

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-- Your access point's SSID and password
local SSID = "xxxxxx"
local SSID_PASSWORD = "xxxxxx"

-- configure ESP as a station
wifi.setmode(wifi.STATION)
wifi.sta.config(SSID,SSID_PASSWORD)
wifi.sta.autoconnect(1)

local TWILIO_ACCOUNT_SID = "xxxxxx"
local TWILIO_TOKEN = "xxxxxx"

local HOST = "iot-https-relay.appspot.com" -- visit http://iot-https-relay.appspot.com/ to learn more about this service
                                           -- Please be sure to understand the security issues of using this relay app and use at your own risk.
local URI = "/twilio/Calls.json"

function build_post_request(host, uri, data_table)

     local data = ""

     for param,value in pairs(data_table) do
          data = data .. param.."="..value.."&"
     end

     request = "POST "..uri.." HTTP/1.1\r\n"..
     "Host: "..host.."\r\n"..
     "Connection: close\r\n"..
     "Content-Type: application/x-www-form-urlencoded\r\n"..
     "Content-Length: "..string.len(data).."\r\n"..
     "\r\n"..
     data

     print(request)

     return request
end

local function display(sck,response)
     print(response)
end

-- When using send_sms: the "from" number HAS to be your twilio number.
-- If you have a free twilio account the "to" number HAS to be your twilio verified number.
local function make_call(from,to,body)

     local data = {
      sid = TWILIO_ACCOUNT_SID,
      token = TWILIO_TOKEN,
      Body = string.gsub(body," ","+"),
      From = from,
      To = to
     }

     socket = net.createConnection(net.TCP,0)
     socket:on("receive",display)
     socket:connect(80,HOST)

     socket:on("connection",function(sck)

          local post_request = build_post_request(HOST,URI,data)
          sck:send(post_request)
     end)
end

function check_wifi()
 local ip = wifi.sta.getip()

 if(ip==nil) then
   print("Connecting...")
 else
  tmr.stop(0)
  print("Connected to AP!")
  print(ip)
     -- make a call with a voice message "your house is on fire"
  make_call("15558976687","1334856679","Your house is on fire!")
 end

end

tmr.alarm(0,2000,1,check_wifi)