If your answer is factory reset, please skip this question.
User reported a problem for iPhone 7.
On iOS 11.0.2, outgoing phone call can be made but no incoming phone call could be made.
On iOS 11.0.3, the situation is reverse. No outgoing phone call could be made whereas sometimes incoming phone calls can be made.
However, if the user dials a USSD code which is carrier-specific, it will be OK to dial an outgoing call for once.
Already contacted the carrier and the SIM card is fine on another Android phone or iPhone.
How to fix without factory reset?
Phone call is a basic feature of a smartphone and I have not encountered similar problem in any Android phones.