In New Zealand I run my phone on SparkNZ, who sent me an email that included this line;

It looks like the device you’re using relies on 3G for some functions, so it’s important you use our device checker to confirm whether you need to replace your device to stay connected.

As far as I know, the only function 3G has on my phone is when there isn’t a 4G network - which is surely a Spark issue, not a phone issue?

Or am I missing something?

If I am not - doesn’t this seem a bit scammy? …

OOHH OOHH - you need to upgrade your phone in case it stops working …. here’s a link to do that.