Phone Hacks

211 Articles

A Working Intercom From Antique Telephones

February 9, 2026 by 13 Comments

Although it can be hard to imagine in today’s semiconductor-powered, digital world, there was electrical technology around before the widespread adoption of the transistor in the latter half of the 1900s that could do more than provide lighting. People figured out clever ways to send information around analog systems, whether that was a telegraph or a telephone. These systems are almost completely obsolete these days thanks to digital technology, leaving a large number of rotary phones and other communications systems relegated to the dustbin of history. [Attoparsec] brought a few of these old machines back to life anyway, setting up a local intercom system with technology faithful to this pre-digital era.

These phones date well before the rotary phone that some of us may be familiar with, to a time where landline phones had batteries installed in them to provide current to the analog voice circuit. A transformer isolated the DC out of the line and amplified the voice signal. A generator was included in parallel which, when operated by hand, could ring the other phones on the line. The challenge to this build was keeping everything period-appropriate, with a few compromises made for the batteries which are D-cell batteries with a recreation case. [Attoparsec] even found cloth wiring meant for guitars to keep the insides looking like they’re still 100 years old. Beyond that, a few plastic parts needed to be fabricated to make sure the circuit was working properly, but for a relatively simple machine the repairs were relatively straightforward.

The other key to getting an intercom set up in a house is exterior to the phones themselves. There needs to be some sort of wiring connecting the phones, and [Attoparsec] had a number of existing phone wiring options already available in his house. He only needed to run a few extra wires to get the phones located in his preferred spots. After everything is hooked up, the phones work just as they would have when they were new, although their actual utility is limited by the availability of things like smartphones. But, if you have enough of these antiques, you can always build your own analog phone network from the ground up to support them all.

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Limiting Battery Risk On Repurposed Smartphones With PostmarketOS

February 1, 2026 by 28 Comments

PostmarketOS is a Linux distribution specifically designed for those who wish to repurpose old smartphones as general-use computers, to a degree. This can be a great way to reuse old hardware. However, for [Bry50], it was somewhat discomforting leaving the phone’s aging lithium battery perpetually on charge. A bit of code was thus whipped up to provide a greater measure of safety.

The concept is simple enough—lithium batteries are at lower risk of surprise combustion events if they’re held at a lower state of charge. To this end, [Bry50] modified the device tree in PostmarketOS to change the maximum charge level. Apparently, maximum charge was set at a lofty 4.4V (100%), but this was reconfigured to a lower level of 3.8V, corresponding to a roughly 40-50% state of charge. The idea is that this is a much healthier way to maintain a battery hooked up to power for long periods of time. There’s one small hitch—the system will get confused if the battery voltage is higher than the 3.8 V setpoint when switching over. It’s thus important to let the device discharge to a lower level if you choose to make this change.

It’s a neat mod that both increases safety, but keeps the battery on hand to let the system ride through minor power outages. If you’re new to the world of repurposing old smartphones, fear not. [Bryan] also has a tutorial on getting started with PostmarketOS for the unfamiliar. If you’re working on your own projects in this space, we’d love to hear about them—so get on over to the tipsline!

Create A Tiny Telephone Exchange With An Analog Telephone Adapter

January 26, 2026 by 15 Comments

An analog telephone adapter (ATA), or FXS gateway, is a device that allows traditional analog phones to be connected to a digital voice-over-IP (VoIP) network. In addition to this, you can even create a local phone exchange using just analog phones without connecting to a network as [Playful Technology] demonstrates in a recent video.

The ATA used in the video is the Grandstream HT802, which features one 10/100 Mbps Ethernet port and two RJ11 FXS ports for two POTS phones, allowing for two phones to be directly connected and configured using their own profiles.

By using a multi-FXS port ATA in this manner, you essentially can set up your own mini telephone exchange, with a long run of Cat-3 possible between an individual phone and the ATA. Use of the Ethernet port is necessary just once to configure the ATA, as demonstrated in the video. The IP address of the ATA is amusingly obtained by dialing *** on a connected phone and picking 02 as menu option after which a synthetic voice reads out the number. This IP address gets you into the administration interface.

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The Nokia N900 Updated For 2025

December 23, 2025 by 15 Comments

Can a long-obsolete Linux phone from 2009 be of use in 2025? [Yaky] has a Nokia N900, and is giving it a go.

Back in the 2000s, Nokia owned the mobile phone space. They had a smartphone OS, even if they didn’t understand app distribution, they had the best cameras, screens, antennas, the lot. They threw it all away with inept management that made late-stage Commodore look competent. Apple and Android came along, and now a Nokia is a rarity. Out of this mess came one good thing, though: the N900 was a Linux-based smartphone that became the go-to hacker mobile for a few years.

First up with this N900 is the long-dead battery. He makes a fake battery with a set of supercapacitors and resistors to simulate the temperature sensor, and is then able to power it from an external PSU. This is refined to a better fake battery using the connector from the original. The device also receives a USB-C port, though due to space constraints, not the PD identifiers, making it (almost) modern.

Because it was a popular hacker device, it’s possible to upgrade the software on an N900. He’s given it U-Boot, and now it boots Linux from an SD card and functions as an online radio device.

That’s impressive hackability and longevity for a phone, if only we could have more like it.

Meet Me On My Rotary Phone

November 14, 2025 by 8 Comments

We suspect kids today — and some adults — are confused about phone terminology. In today’s world, “hanging up” and “dialing,” for example, are abstract words without the physical reference that older people remember. But some people have a soft spot for the old rotary dial phones, including [Stavros], who wired a rotary phone to his computer for use on online meetings. Check out the video below.

He took an old rotary phone and wanted to program a Raspberry Pi Zero to act as a sound card and a keyboard. That way, he could connect to the meeting by picking up the handset and disconnect by hanging up. He also planned to read the dial and convert that into keyboard input.

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2G Gone? Bring It Back Yourself!

October 6, 2025 by 26 Comments

Some parts of the world still have ample 2G coverage; for those of in North America, 2G is long gone and 3G has either faded into dusk or beginning its sunset. The legendary [dosdude1] shows us it need not be so, however: Building a Custom 2G GSM Cellular Base Station is not out of reach, if you are willing to pay for it. His latest videos show us how.

Before you start worrying about the FCC or its equivalents, the power here is low enough not to penetrate [dosdude]’s walls, but technically this does rely in flying under the radar. The key component is a Nuand BladeRF x40 full-duplex Software Defined Radio, which is a lovely bit of open-source hardware, but not exactly cheap. Aside from that, all you need is a half-decent PC (it at least needs USB-3.0 to communicate with the SDR, the “YateBTS”  software (which [dosdude1] promises to provide a setup guide for in a subsequent video) and a sim card reader. Plus some old phones, of course, which is rather the whole point of this exercise.

The 2G sunset, especially when followed by 3G, wiped out whole generations of handhelds — devices with unique industrial design and forgotten internet protocols that are worth remembering and keeping alive. By the end of the video, he has his own little network, with the phones able to call and text one another on the numbers he set up, and even (slowly) access the internet through the miniPC’s network connection.

Unlike most of the hacks we’ve featured from [dosdude1], you won’t even need a soldering iron, never mind a reflow oven for BGA. 

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How Many Phones Sport A 5 And 1/4 Diskette Drive? This One.

September 27, 2025 by 13 Comments

It all started with a sarcastic comment right here on Hackaday.com: ” How many phones do you know that sport a 5 and 1/4 inch diskette drive?” — and [Paul Sanja] took that personally, or at least thought “Challenge accepted” because he immediately hooked an old Commodore floppy drive to his somewhat-less-old smartphone. 

The argument started over UNIX file directories, in a post about Redox OS on smartphones— which was a [Paul Sajna] hack as well. [Paul] had everything he needed to pick up the gauntlet, and evidently did so promptly. The drive is a classic Commodore 1541, which means you’ll want to watch the demo video at 2x speed or better. (If you thought loading times felt slow in the old days, they’re positively glacial by modern standards.) The old floppy drive is plugged into a Google Pixel 3 running Postmarket OS. Sure, you could do this on Android, but a fully open Linux system is obviously the hacker’s choice. As a bonus, it makes the whole endeavor almost trivial.

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