A SIM card that was activated in a 4G device will still work with a 5G device, but you may have trouble connecting to the 5G network. Check with your carrier if you're not seeing the little 5G logo pop up on your screen and you think you should be.
What happens if I put a 4G SIM card in a 5G phone?
5G SIM Cards If a card is activated as 4G LTE and inserted into a 5G device, it can access the 5G Ultra Wideband network but may not connect to the “future enhanced 5G network.”
Can I use a 4G SIM in a 5G router?
Some people are wondering whether they can use 4G SIM card in 5G SIM router. The answer is yes. Almost all 5G CPE in the market support 4G, and many also supports 3G.
Is a new SIM card needed for 5G?
As we mentioned before, to get access to the 5G network you will need a SIM card that works with 5G. It is also possible that you can keep your old phone number if you will continue working with the same carrier.
Will existing 4G SIM cards work with 5G?
4G sim cards works on 4G / 5G phones. Yes. 4G phones still work on a 5G network, they just won't get that superfast 5G speed until 5G sims start rolling out, but it'll still be faster than regular 4G smartphones.