I got Omnia with expectation that I’ll be able to use LTE out of the box thanks to SIM card slot.
However upon getting my hands on it seems to be lacking out-of-the-box LTE support, it just features a SIM cards slot.
Am I wrong or am I just doing something wrong?
How should I proceed to start using the LTE card with the router?
There is only a sim slot on board wired up to mpcie slot. You have to have a modem in that mpcie slot. Then there is some official documentation on how to configure fallback (https://doc.turris.cz/doc/start).
There are also some modem specific pages In Czech section of community documentation (unfortunately they seems to not be translated to en but google translator might help you).
Hm ok, so what modem should I get? I guess I need to be careful which one to buy because of the drivers.
Yes, not all modems have Linux drivers and not all of them has drives in Turris OS. In that Czech section of community documentation are some modems specified but those are connected trough usb.
I would suggest using the one we shipped as part of indiegogo campaign as that one is already tested. You can conveniently see everything that was in package for example in this topic: [SELL] unused Lte modem EU for Turris Omnia / [PRODEJ] nepouzity Lte modem EU pro Turris Omnia.
You can look here on forum for other test results. I know that some users were trying other modems too but I can’t suggest any such modem because I wasn’t tracking any of those tests.
It seems it will be impossible to find that one on EU market at the moment.
Is it possible to use Omnia with LTE only anyway?
No. Technology is dictated by used mpcie card (modem) not by omnia. If there are drivers for some card in Omnia then there are no additional limitations on top of that. LTE (that is what I suspect you meant) is just wireless standard. It has nothing to do with Omnia directly. You can update card in future if you want to switch or update supported bands.
What I am asking is the OS supplied by the Omnia able to route LTE to local WIFI. Is this setup possible?
Also, how to handle antennas when using LTE modem?
It’s pretty easy to get one copy:
https://m.ebay.de/itm/1Pcs-For-Quectel-EC20-LTE-WWAN-modem-2G-3G-4G-mini-PCIe-Card-EC20AA-256-STD-/263189547727
Even pricing of 60€ in total seems OK…
But cannot tell the difference to https://m.ebay.de/itm/1Pcs-For-Quectel-EC20-E-LTE-WWAN-modem-2G-3G-4G-mini-PCIe-Card-EC20EA-256-STD-/272835725768 for 210€…
I need antenna too? And drill hole for it?
Yes, you need antennas. There’s no problem in getting them online. Which country are you located in?
And you need same amount UFL/pigtail-RPSMA-cabling to connect card and antennas (if using RPSMA-antennas) .
Drilling holes: Omnia has 5 holes predrilled of which 2 are in standard-configuration covered/unused and 3 are in use with the three preinstalled antennas (for using the preinstalled 3x3 bgnac-card combined with the preinstalled 2x2 bgn-card using the two diplexers)
As that linked card needs three antennas you need to drill one additional hole if using standard-configuration.
In my usage scenario it would be a little bit different - I run a 4x4 ac-card combined with the preinstalled 3*3 bgnac-card via three diplexers and therefore only one unused hole is actually left.
Drilling is pretty easy, I already drilled 2 additional holes for my second Omnia 
How many antennas do I need?
See my text above: do you have standard configuration atm? If yes then you need for the linked PCIe-card to