For the 21700 cell if you want to do this without spending a lot on batteries, but also be sure that any misconfigured hardware can't drain the battery below a damage threshold, use a button top protected 21700 cell. Here's a good 'house brand' one that is popular with 21700 flashlights.

https://liionwholesale.com/collections/batteries/products/pr...

Lovely job, I like the "here's where I've got to so far" style. This gives people enough to work from and make a hand-wired version while he's waiting for boards to come back. Even if he runs out of time to do anything it's leaving a working design and firmware for folk to start from.

It's definitely too easy to put off publishing until it's "properly" done and then it never happens.

I remember someone building this (couple of years ago) https://skysedge.com/telecom/RUSP/index.html I so wish this was an actual product.

When I finally agree to cave in and buy a phone for my soon-to-be teenager, little does she know this is the phone I have in mind…

i wouldn't want my child making unencrypted calls :p

It's no more or less encrypted than any cellular phone making a call across your local 3GPP-whatever standard network.

Doesn't this project go straight into modern standard mobile phone systems? It'll be encrypted then.

I think he might have been calling into question the wisdom of using the standard telephone network to directly place voice calls. Technically it's encrypted but your privacy is anything but guaranteed.

Love seeing old tech brought back to life like this. The tactile experience of dialing is just something else.

Slightly off topic but you can also use a SLIC module to talk to old phones:

https://youtu.be/nibV_idJjlg

https://www.ebay.com.au/itm/305557776577

This project uses the same AG1171 SLIC module; it's just not enough by itself and still requires a microcontroller (or at least non trivial logic) even before you get to processing the audio streams.