There are lots of occasions when it would be useful to know your iPhone's SIM number.
You could be asked to provide it when registering your phone, changing phone number, accessing online services from your mobile network or for other verification reasons. It is also useful to know it in case your iPhone gets stolen.
We would therefore suggest you take note of it now; you're likely to need it in future, and in the case of theft, you won't be able to find the ICCID easily after disaster strikes.
