Update to iPhone carrier settings?

[Feek]

I've just had this appear on my screen:

Does anyone know what this does? What's it actually updating?

If I cancel it now, will I get offered it again?

 

[Feek]

Yes, that link is what you get when you click on the Learn More button, but it doesn't really say anything.

 

[Feek]

It's no different to when they first got their iPhone, the default settings are not correct for PAYG customers.