Koppar releases USB-C LTE modem for computer phone line
Open-source 4-layer board design lets a computer make calls, send texts, and receive LTE data over a single USB-C cable.
What to know
- A developer has published an open-source, manufacturable design for a USB-C LTE modem board that gives any computer phone line capabilities—calls, SMS, and LTE data—through a single cable.
- The board uses Koppar AI's design-from-spec service to move from a one-page specification to a complete 4-layer KiCad design with gerber files and assembly BOMs for JLCPCB.
- Early discussion centers on VoLTE dependency: the device relies on 2G/3G or VoLTE to function, and carrier whitelisting may be required; 2G/3G networks are being shut down globally.
- Skepticism exists about whether the design has been built and tested in practice, though the creator has provided detailed technical documentation and design rationale.
The dispute Whether the board design is practical and has been validated through actual construction and testing, versus being a theoretical design that has not been built. · positions read across 5 posts and comments
The design is interesting and solves a real problem, but testing and long-term carrier support are critical unknowns.
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“This is great. Apple needs to figure out how to fit one into a 16" MacBook Pro.”
mcculley · Hacker News ↗
The project is likely untested and AI-generated, raising doubts about whether it would actually work if built.
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“Obviously AI vibed, which means the project probably has never been built and wouldn't work if you built it.”
Vaushite · Hacker News ↗
abijahkaj Hardware designer / project creatorKoppar AI Design-to-manufacturing service
How it unfolded 6 developments, newest first · click a bar or a number to jump articlespostscomments
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6
Creator addresses VoLTE support and carrier dependency
The developer clarifies that the Quectel EC25-EUX modem natively supports VoLTE, and the audio path is identical regardless of whether calls use VoLTE or 2G/3G fallback. However, VoLTE support in practice depends on carrier whitelisting and the correct carrier MBN profile being loaded on the module, not on the PCB design itself.
“Yes, the Quectel EC25-EUX supports VoLTE natively on the modem baseband, and from the board's perspective the audio path is identical: the modem handles the IMS/SIP registration and AMR codec internally and outputs standard 1.8V PCM digital audio to the RP2040 whether the call is over VoLTE or 2G/3G fallback.”
— abijahkaj -
Yes, the Quectel EC25-EUX supports VoLTE natively on the modem baseband, and from the board's perspective the audio path is identical: the modem handles the IMS/SIP registration and AMR codec internally and outputs standard 1.8V PCM digital audio to the RP2040 whether the call is over VoLTE or 2G/3G fallback.I put that caveat in the README because…
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Commenter flags VoLTE dependency as major limitation
A user raises concerns about the board's reliance on VoLTE support, warning that 2G/3G deprecation by carriers could render the device non-functional without proper carrier whitelisting and firmware.
“This is a huge caveat. OP, does your setup even support VoLTE? Otherwise this might become a brick in a few years as your carrier shuts down 2G/3G, as many carriers around the world have already done…”
— gruez -
>Where 2G and 3G are switched off, calls need a module firmware with VoLTE and a carrier that allows it; ask the seller.This is a huge caveat. OP, does your setup even support VoLTE? Otherwise this might become a brick in a few years as your carrier shuts down 2G/3G, as many carriers around the world have already done
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4
Developer expresses interest in hardware integration
A commenter suggests the modem concept should be integrated into MacBook Pro hardware.
“This is great. Apple needs to figure out how to fit one into a 16" MacBook Pro.”
— mcculley -
3
Skeptic questions whether design has been built and tested
A commenter expresses doubt about the project's feasibility, suggesting it may be AI-generated and untested.
“Obviously AI vibed, which means the project probably has never been built and wouldn't work if you built it.”
— Vaushite -
Obviously AI vibed, which means the project probably has never been built and wouldn't work if you built it.
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2
Creator explains motivation and technical architecture
The developer clarifies the design goals: enabling real phone line functionality on a computer (calls and texts on a physical SIM), with call audio handled through a USB sound card implemented by an RP2040 microcontroller. The RP2040 bridges the modem's 1.8V PCM audio through a level shifter to handle audio in and out over USB.
“I wanted a real phone line on my computer: calls and texts on a physical SIM, answered through my headset at my desk, or by a script or an AI agent when I'm away.”
— abijahkaj -
I wanted a real phone line on my computer: calls and texts on a physical SIM, answered through my headset at my desk, or by a script or an AI agent when I'm away. Cloud numbers get treated as VoIP, and old Android phones give you no clean way to get call audio in and out over USB.So this is a 4-layer USB-C board around a Quectel EC25-EUX. Behind a…
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Koppar-designed USB-C LTE modem board released as open source
A developer posts a complete, open-source design for a USB-C LTE modem on GitHub. The 4-layer board connects to a computer through a single USB-C cable and provides phone line functionality: LTE data, SMS, and voice calls with audio routed through USB. The design includes gerber files, BOMs, and assembly instructions for JLCPCB manufacturing.
“A phone line over USB-C: LTE data, SMS and voice calls with the call audio on USB. A 4-layer KiCad board designed by Koppar from a one-page spec.”
— Project description -
first by HN Frontpage, 11d ago
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What people are saying 0 voices from 0 sites · best of 5 · verbatim
- Has this board actually been built and tested end-to-end?
- Will it work reliably on carriers that have already shut down 2G/3G networks, and how easy is VoLTE setup?
- What is the role of AI in this design—was it AI-generated or just AI-assisted?