I just take my SIM that has the data package only enabled and put it in a USB modem, plug that into the OpenWRT build called Rooter from OfModemsAndMen.com loaded onto a $25 GL-AR150 from Amazon and I share the connection among all the nearby devices including the tablet where I removed the SIM. Works flawlessly.
*** P.S. When buying a cheap used USB modem on eBay, pay attention to the modem suffix after the model number because the same model is sold in different countries with different supported bands, the suffix indicates which bands it supports. The USBmodem/Rooter combo is normally cheaper than buying a mifi device and supports different country bands, as stated.
**** PPS Also note that a number of 4M routers are also supported including the ($7 US) A5-V11 (plus some model clones) and with full Luci interfaces as well as support for all listed modems, plus there is the option of other routers that the package lists, 4M, 8M and higher.
******* PPPS I personally use the more expensive 8M GL-AR150 because it provides room for other Optware packages like OpenVPN and ad blocking packages with a pixel jpg server, plus a printer and other packages. However I also have several A5-V11 clones which run this basic Rooter port of OpenWRT quite well and my modems work just as well on those. The A5-V11 has about a 40% higher current draw than the GL model but usually no sweat for a typical interface to run the modem and router with 500mA. If you buy the A5-V11 clones on eBay, it's a chance you'll get the correct one or one that can easily take the OW upgrade. Shoot for the black model that says "3G Router 150M" and if you can read the label on the back the password is "12345678" to increase your chances of receiving a OpenWRT flashable device. (Note the 3G means nothing with the new firmware and 4G is supported.) Also note that you cannot flash OpenWRT directly to many of these A5-V11 clones, you have to telnet and use the MTD command to replace both the bootloader with OW compatible and kernel with a mini version of OpenWRT (preferably with Luci and DHCP) and from that interface you then do a normal firmware upgrade to the Rooter version of OpenWRT.
(Last edited by DonJuane on 17 Feb 2018, 18:55)