--- title: Show HN: A USB-C LTE modem that gives my computer a... description: This open hardware project is a 4-layer KiCad board that gives a computer its own phone line over USB-C. It exposes LTE data, SMS and voice calls, with call... canonical: https://daily.dev/posts/show-hn-a-usb-c-lte-modem-that-gives-my-computer-a-phone-line-ndbgdb1vw twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Show HN: A USB-C LTE modem that gives my computer a phone line | daily.dev og:description: This open hardware project is a 4-layer KiCad board that gives a computer its own phone line over USB-C. It exposes LTE data, SMS and voice calls, with call... og:url: https://daily.dev/posts/show-hn-a-usb-c-lte-modem-that-gives-my-computer-a-phone-line-ndbgdb1vw og:image: https://api.daily.dev/og/posts/ndbGDB1Vw.png og:image:alt: Show HN: A USB-C LTE modem that gives my computer a phone line og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Show HN: A USB-C LTE modem that gives my computer a phone line **[Hacker News](https://daily.dev/sources/hn)** · 6 min read · 0 upvotes · 0 comments ## Summary This open hardware project is a 4-layer KiCad board that gives a computer its own phone line over USB-C. It exposes LTE data, SMS and voice calls, with call audio delivered as a USB sound device. The design uses a Quectel EC25-EUX modem and an RP2040 for audio, drawing 5V from USB-C with a 3.8V/3A buck for the modem's transmit bursts. Rev A had a 35 ohm antenna feed, a buck 60mm from its inductor, and a backwards SIM socket; rev B fixes all three and passes with 0 DRC errors. The board, Gerbers, BOM and design review are released under the CERN Open Hardware Licence v2. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Which Quectel EC25 variant do I need for voice calls over USB, not just data? You need the EC25-EUX variant, ordering code EC25EUXGR-128-SGNS (the EC25EUXGA-128-SGNS is end-of-life but shares the same LGA-144 footprint). North American EC25 data-only variants do not support voice, so the EUX is required specifically for voice calling alongside LTE data. _Developers sourcing LTE modules for voice-capable hardware track part compatibility notes like this on daily.dev._ ### Can a USB-A port or a 1.5A power source run an LTE modem like the Quectel EC25 reliably? No, a USB-A port or 1.5A source will brown out during a 2G transmit burst. The board uses 5.1kOhm CC resistors to negotiate as a sink without active negotiation, so it needs a USB-C cable and port able to supply the full 3A at 5V the module's 2A transmit bursts require. _Engineers planning power budgets for cellular modules can check real-world draw figures like these on daily.dev._ ### How do I recover an RP2040 board that has no BOOTSEL button after a bad firmware flash Short the BOOT and GND pads while plugging the board in, which brings the RP2040 up as a USB drive for a new .uf2 file, even if the previous firmware crashes before USB starts. A blank RP2040 boots into its USB bootloader automatically without needing this step. _Developers debugging RP2040 bring-up and recovery flows compare board designs like this on daily.dev._ ## Community take How the wider developer community reacted, aggregated from 1 discussion and 46 comments across hackernews (as of 2026-10-31). **TL;DR:** The hardware itself drew interest (including a suggestion Apple should add this to MacBooks), but discussion mostly drifted into whether LTE/VoLTE will remain supported long-term and skepticism about the AI-assisted design process. **Sentiment:** 30% positive · 45% mixed · 25% skeptical **The case for** - Some see genuine utility in a dedicated phone-line board for desk setups and scripted/AI call handling. - One commenter said it could be useful since routing 911 over cellular would be free versus a VoIP provider's surcharge. - Praise for wanting this kind of functionality built into laptops like the MacBook Pro. **The pushback** - Concern that the design was 'AI vibed' and may not have been built or work as intended. - The PCB routing looked erratic/over-engineered to one viewer, questioning the autorouting quality. - Worry that without confirmed VoLTE support, the device could become useless once carriers shut down 2G/3G. - Debate over whether LTE will remain supported long-term as 5G/6G networks evolve, with some predicting carriers will decommission LTE core infrastructure. **By community** - hackernews (mixed): Interest in the hardware project was mixed with a long tangent on LTE's future and skepticism about AI-generated design quality and VoLTE support. **Hottest debate:** Whether LTE will keep working long-term as carriers move to 5G/6G, versus the claim that OFDM allows indefinite backward compatibility. **Open questions** - Does the board's modem firmware actually support VoLTE, which would be needed once 2G/3G networks are retired? - Has the board actually been built and tested, or does it only exist as an AI-generated design so far? **Highlights** > Obviously AI vibed, which means the project probably has never been built and wouldn't work if you built it. > — [Vaushite on hackernews · 1 comments](https://news.ycombinator.com/item?id=50319590) > I mentioned in the top comment that Koppar generated the board and that the first batch is about to be ordered, so no detective work needed there. I'm just as skeptical of blind AI hardware output as you are, which is why I audited every net against the datasheets and put all the flaws in REVIEW.md in the repo before ordering: - The 0.33 mm RF trace came out to ~35 Ω instead of 50 Ω and hopped layers through vias (I included Pi-matching pads to tune it on the bench). - The 3.8 V buck converter was placed too far from its inductor, and the 1.37 mm power trace is narrower than Quectel's 2 mm recommendation (~100 mV drop at 3 A). - The SIM socket (J2) is oriented inward, which is annoying mechanically. 5 bare boards + 2 PCBA units are currently being ordered at JLCPCB, and I'll order the EC25-EUX modules separately to hand-solder onto U8 since JLC was out of stock. Since the KiCad files are in the repo, if you spot a specific net or pinout error that will brick bring-up, let me know so I can bodge-wire it next week. > — [abijahkaj on hackernews · 1 comments](https://news.ycombinator.com/item?id=50319688) > The PCB looks super weird, what is going on here? https://files.catbox.moe/nijoin.png https://files.catbox.moe/suazr4.png They sort of look sensible until you look closer and then the whole board is fever dream autorouting. > — [drum55 on hackernews · 1 comments](https://news.ycombinator.com/item?id=50319828) > >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 > — [gruez on hackernews](https://news.ycombinator.com/item?id=50320356) > This is great. Apple needs to figure out how to fit one into a 16" MacBook Pro. > — [mcculley on hackernews · 1 comments](https://news.ycombinator.com/item?id=50319990) **Source threads** - [hackernews](https://news.ycombinator.com/item?id=50317331) · 32 points · 46 comments ## Similar posts on daily.dev - [This Tiny USB Device Turns Your Phone Into a Keyboard, Mouse, and SSH Terminal](https://daily.dev/posts/this-tiny-usb-device-turns-your-phone-into-a-keyboard-mouse-and-ssh-terminal-gcmljxb1j) · It's Foss · 5 upvotes · 0 comments - [Converting a $20 4G wireless hotspot into a texting device](https://daily.dev/posts/converting-a-20-4g-wireless-hotspot-into-a-texting-device-e0hns3ftf) · Lobsters · 0 upvotes · 0 comments - [Openterface KeyMod turns your smartphone into a USB keyboard, mouse, gamepad, or SSH client \(Crowdfunding\)](https://daily.dev/posts/openterface-keymod-turns-your-smartphone-into-a-usb-keyboard-mouse-gamepad-or-ssh-client-crowdfu-lgzfv0lpp) · CNX Software · 0 upvotes · 0 comments - [Turning An Old Phone’s Motherboard Into An RC Plane Controller](https://daily.dev/posts/turning-an-old-phone-s-motherboard-into-an-rc-plane-controller-tzlsseyup) · Hackaday · 0 upvotes · 0 comments - [Using ThinkPad T480 as a mobile phone](https://daily.dev/posts/using-thinkpad-t480-as-a-mobile-phone-taaxnlzzv) · Hacker News · 0 upvotes · 0 comments --- [View this post on daily.dev](https://daily.dev/posts/show-hn-a-usb-c-lte-modem-that-gives-my-computer-a-phone-line-ndbgdb1vw) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Show HN: A USB-C LTE modem that gives my computer a phone line","url":"https://daily.dev/posts/show-hn-a-usb-c-lte-modem-that-gives-my-computer-a-phone-line-ndbgdb1vw","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/show-hn-a-usb-c-lte-modem-that-gives-my-computer-a-phone-line-ndbgdb1vw"},"datePublished":"2026-10-31T21:52:21.116Z","dateModified":"2026-10-31T21:52:57.049Z","description":"This open hardware project is a 4-layer KiCad board that gives a computer its own phone line over USB-C. It exposes LTE data, SMS and voice calls, with call...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/9c3d5bb6bf14d9929d8aff28bfc6a1a7?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/9c3d5bb6bf14d9929d8aff28bfc6a1a7?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Hacker News","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Hacker News","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/hn","url":"https://daily.dev/sources/hn"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/show-hn-a-usb-c-lte-modem-that-gives-my-computer-a-phone-line-ndbgdb1vw","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"","timeRequired":"PT6M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Hacker News","item":"https://daily.dev/sources/hn"},{"@type":"ListItem","position":3,"name":"Show HN: A USB-C LTE modem that gives my computer a phone line"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/show-hn-a-usb-c-lte-modem-that-gives-my-computer-a-phone-line-ndbgdb1vw#faq","mainEntity":[{"@type":"Question","name":"Which Quectel EC25 variant do I need for voice calls over USB, not just data?","acceptedAnswer":{"@type":"Answer","text":"You need the EC25-EUX variant, ordering code EC25EUXGR-128-SGNS (the EC25EUXGA-128-SGNS is end-of-life but shares the same LGA-144 footprint). North American EC25 data-only variants do not support voice, so the EUX is required specifically for voice calling alongside LTE data. Developers sourcing LTE modules for voice-capable hardware track part compatibility notes like this on daily.dev."}},{"@type":"Question","name":"Can a USB-A port or a 1.5A power source run an LTE modem like the Quectel EC25 reliably?","acceptedAnswer":{"@type":"Answer","text":"No, a USB-A port or 1.5A source will brown out during a 2G transmit burst. The board uses 5.1kOhm CC resistors to negotiate as a sink without active negotiation, so it needs a USB-C cable and port able to supply the full 3A at 5V the module's 2A transmit bursts require. Engineers planning power budgets for cellular modules can check real-world draw figures like these on daily.dev."}},{"@type":"Question","name":"How do I recover an RP2040 board that has no BOOTSEL button after a bad firmware flash","acceptedAnswer":{"@type":"Answer","text":"Short the BOOT and GND pads while plugging the board in, which brings the RP2040 up as a USB drive for a new .uf2 file, even if the previous firmware crashes before USB starts. A blank RP2040 boots into its USB bootloader automatically without needing this step. Developers debugging RP2040 bring-up and recovery flows compare board designs like this on daily.dev."}}]} ```