ComputerCraft Lua cell tower [WIP]

--[[
Made by Michal Nemecek. Please do not redistribute.
]]--
rednet.open("back")
while true do
    phout = nil
    phexists = false
    id,msg = rednet.receive()
    rs = msg:sub(1,1)
    if rs == "R" then
        if tonumber(msg:sub(2,10)) ~= nil and tonumber(msg:sub(11)) ~= nil then
            for line in io.lines("phonebook.txt") do
                if line:sub(1,9) == msg:sub(2,10) then
                    phexists = true
                    break
                end
            end
        end
        if not phexists then
            io.close("phonebook.txt")
            io.open("phonebook.txt","a")
            io.write(msg:sub(2))
        end
    elseif rs == "S" then
        for line in io.lines("phonebook.txt") do
            if line:sub(1,9) == msg:sub(2,10) then
                phexists = true
                phout = line:sub(10)
                rednet.send(tonumber(phout),msg:sub(11))
            end
        end
    end
end