SIM cards from the 3G UMTS network onwards are backwards and forward compatible, and mobile phones are backwards compatible. So, a 5G SIM card will work in a 4G phone, but will only allow you to access 4G, 3G and 2G networks if used in a 4G phone .
SIM cards from the 3G UMTS network onwards are backwards and forward compatible, and mobile phones are backwards compatible. So, a 5G SIM card will work in a 4G phone, but will only allow you to access 4G, 3G and 2G networks if used in a 4G phone .