SMS-based ChatGPT for low-tech folks

Motivation •

Recently I went low-tech, and I’ve been super happy with Light Phone II’s very limited capabilities^[1] besides texting and calling.

One thing was missing though: ChatGPT. I’ve gotten used to querying random stuff, and wanted a way to access it from my dumb phone.

So I thought — wait a minute. We have all the technology available to build this.

The concept •

1. text a number with a question
2. run a serverless function that calls OpenAI API with some preset rules
3. text back with an answer.

Making it happen •

Obviously, I had a short chat about it with ChatGPT, and then started coding with Cursor. There are a few pre-requisites for this, and it costs money.

We don’t need much to set this up:

1. Write and deploy the serverless handler^[2] (see code below)
2. Get your OpenAI API key and upgrade to a paid plan
3. Get a paid Twilio plan and buy a phone number^[3]
4. Set up webhook URL in Twilio dashboard to point to your API endpoint.

Somewhat abbreviated:

const twilio = require('twilio')
const { OpenAI } = require('openai')

const openai = new OpenAI({ apiKey: process.env.OPENAI_API_KEY })

const twilioClient = twilio(
  process.env.TWILIO_ACCOUNT_SID,
  process.env.TWILIO_AUTH_TOKEN
)

const sendSMS = (to, body) => twilioClient.messages.create({
  body,
  to,
  from: process.env.TWILIO_PHONE_NUMBER
})

module.exports = async (req, res) => {
  try {
    const { Body, From } = req.body

    if (From !== process.env.ALLOWED_PHONE_NUMBER) {
      return res.status(403).end()
    }

    const completion = await openai.chat.completions.create({
      model: 'gpt-4o',
      messages: [
        {
          role: 'system',
          content: 'please provide concise answers under 160 characters.'
        },
        { role: 'user', content: Body }
      ],
      max_tokens: 60
    })

    await sendSMS(From, completion.choices[0].message.content)

    return res.status(200).end()
  } catch (error) {
    return res.status(500).end()
  }
}

I do some error handling as well, but that’s about it. Here’s the full source code.

Caveats •

I still don’t know how much this will cost, I’ve added some estimates to the repo readme, but Twilio pricing is highly dependent on location.^[4]

Also, not too conveniently, the reply comes from a different number than the one I have to text. This could be because my reserved number is not local. I will figure this out soon and update accordingly.

Is it worth it? •

For me, absolutely! I have a way to ask ChatGPT questions, and I don’t even need an internet connection for that. This could have a lot of other potential use cases where internet connection is limited or not available.