Hi, I use my SIM in my 5g router regularly when I go away. You can't clone a sim card, but if you have an apple or Samsung watch you could get a plan to keep connected for calls n texts depending on your network provider when you are using the SIM in your router. This costs about £7 extra a month. Other option is grab a cheap sim costs an extra £3 a month for calls etc and you can forward calls to it from your unlimited SIM. You would still need to log into router to read and reply to your SMS if you did the latter.
Finally if you have a duel SIM phone and are not in contract, plus depending on your signal strength, (this is what I have set up): silux mobile unlimited data SIM 2 yr contract £11.95pm (uses three) and a rwg mobile SIM for calls/texts (uses ee) 1 yr pre paid unlimited calls n text and 5gb data £40 for the year £3.33 a month pro rata. Works out £15 a month but ultimate flexibility and keep connected when data SIM is in router
