Hi,
To get the unit registered with Skoda you will either need to:
a) put in a sim card with an active data plan
b) connect the columbus unit to a WIFI source in the settings
c) connect a mobile phone which can share the data connection (pretty sure there is a setting somewhere to allow the data apps on the unit to use your mobile connection)
you should then be able to register the device with your MySkoda account.
If you want the live services when you are out and about (and registered) you can indeed just pop a data sim in and it should connect. You'll notice a red globe / circle at the top middle of your columbus screen, this will go white when connected to the mobile network.
Not 100% sure if the tethered mobile phone option will work for this as well? I have a sim card in mine (but I don't subscribe to the live services as I use Apple CarPlay which does pretty much everything I need) but its there as a handy backup.
I used a sim card from RWG mobile (EE network), They used to have a "free" sim which gave 50 minutes, 50 SMS and 250mb a month for an initial top up of £5 then free after that, but that offer has gone now. Their "free" sim is now an initial top up of £15 which gives you 100 minutes / 100 SMS and 750MB of data which is then free after the first month. Could still be an option for you. https://www.rwgmobile.wales/rates-plans-eng-per/ and look for the "free £15" sim.
Hope this helps.
Slick2097.