As far as I understand there are m.2 modules for cellular connection used in some notebooks. Can I attach such a thing into rock5b and magically turn it into a phone?
Radxa phone with cellular module
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I searched the subject for a while, and my current understanding is that:
- bottom M.2 slot is B key and is connected to PCI-3 lanes, suitable for NVMe
- top M.2 slot is E key (making it particularly suitable for Wifi module)
One thing to be aware is what protocol the cellular module is using to make sure it will be able to communicate in the slot.
For me I came to conclusion I would use M.2 cellular module with an USB adapter.
My reason is because I need NVMe + Wifi/BT + 4G at the same time.
Now my concern is choosing one LTE M.2 module (Cat 6 and above) among models like: Quectel EP06, Sierra Wireless EM7455/MC7455, Fibocom 850/860 GL just to name a few…
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I think it should be possible. I plan to test a few things out like this myself, but IMO the form factor is a little too big for a phone.
It would be good for prototyping though.
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particularly for me, the form factor is great
I was planning to replace my phone with a tablet that can make cellular calls.
With this power it should be able to replace my laptop also.
And then what will be missing is adding an epaper second screen and EMR sensor board for handwriting. 
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@Etienne , @NaheemSays I want to buy a module and wanted to check with you. Did you try anything yet?
I am not experienced so I thought trying something that is known to work would be good, so I checked pinephone page. They are using cat 4 modem with VoLTE support. Quectel_EG25-G_LTE_Specification_V1.0.pdf (pine64.org)
I am trying to compare to Quectel Ep06 but it does not have a simcard slot 
Probablly that will not have the performance of cat6 modem. But first I want it to work, and then preferably be fast. Probably I will need driver and Android RIL implementation. (I have no idea what I am talking about).
I am not sure if you can make voice calls with a device that does not have VoLTE tag on it.
If you guys have think I am doing a mistake and I should strongly consider other options, then please stop me from making a mistake
@Etienne when going over modems I saw few that work as LTE+WiFi modems.
One more point: where do I stick the simcard? Most of the modems dont seem to have slot for it.
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Maybe a usb modem suck as Quectel EC20 can work ?
I use a EC20 USB dongle to connect 4G cellular network.
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There is not enough space for on the top for a M2 to mpcie adapter, so the most useful method will not work.
I tried using the adapter via a mpcie to USB and it was detected, but I have not tested more than that.
The adapter was a £10-ish used sierra wireless airprime (MC7355 Qualcomm 4G) that I had ordered off of aliexpress. Not sure how it will work if connected to a mic and phone app, I just tested if it was detected and it was.
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Can you link such hw, epaper and emr to make a secondary screen for handwriting?
Or you’re just using your imagination? 
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Not aware of an existing one. It is mainly my weird imagination. Trying to put everything in one place. But first I need to cellular communication part
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Didn’t make my choice yet but I’ve read many good opinions on GL-iNet brand which are selling openwrt friendly LTE portable routers.
Looking at their MUDY product page, they propose either cat4 or cat6 versions of LTE modules (like the Quectel EP06).
Regarding lack of simcard slot it is expected in M-2 form-factor. You get it with the adapter (like m.2 USB adapter for instance) or on the board directly
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I ended up ordering 2 devices. EM12-G and EG25-G.
Hope I can get them working, especially because the second one is used in pinephone.
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If anybody interested in results
I got the modules and tried EG25-G
So I could make 4G internet to work without much problem. I can send SMS, initiate calls. I have not set it up to be able to talk over the phone. yet.
Also I have checked on ubuntu and armbian, havent checked on android yet.
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Aaaaand POC is done. I had my first phone conversation over Radxa Rock5b.
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Hello, do you have many details please, the card is mini pci express has a sim, how does the internet work, what antennas, what drivers, a link please.
Thank you!
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I could initiate SMS, used 4G internet (as mentionned in feb 19 message), and cellular voice conversation. All phone functionality is working. I am on Armbian, also tried on Radxas Ubuntu.
But I need to make it accessible, in a more phonelike UI. May be I will prepare some tutorial. My end goal is to make tablet that works as phone and notebook.
I also installed Modem Manager GUI in Armbian to see what commands it has, but since I don’t have the card in the system, I can’t really see much… I found on aliexpress EG25-G with mini pcie interface, does it work in mini pcie interface or with an adapter? What firmware needs to be installed? I ordered an EG25-G board anyway.
You need a usb adapter for that one, rock5b does not have a slot you can put that in.
I have been searching for a card that I can directly put on the 5b, and which also has simcard slot. I could not find it. If you know of one that directly fits, I would like to learn from you.
Would this not work: https://www.mouser.com/ProductDetail/Soracom/4573326591584?qs=Y0Uzf4wQF3l6IoiWo78D0g%3D%3D ?
I took this and it is on the SIM card:
https://www.aliexpress.com/item/32951096006.html?spm=a2g0o.order_list.order_list_main.17.21ef1802G4Cmab
you see boards with sim and that eg25 and also see some riser to include both
only cannot get much of price some are expensive and some are cheap