This isn't to do with LFS itself so I'm not sure if it's technical assistance, but hey I'll put it here.

If I enter my mobile number for SMS updates or whatever in LFS, and I'm not in the country I am registered as on LFSWorld (e.g. in Greece) would it work?

The SMS should reach your phone from LFS World, as long as the phone number is correct and reachable.

It is not related to the country you registered with, only the phone number.

Thanks. I guess that this feature could be rather useful