As per the title. 

My wife's iPhone X has (up until a day or so ago) been using her phone number as the main connection point for iMessage and FaceTime. 

Now - all messages are going through as SMS. This means that she's not receiving iMessages, unless she activates it as he email address, which is not the preferred contact. 

FaceTime is also playing up. 

Have followed every troubleshooting tip and trick and simply cannot get this darn iPhone to connect to iMessages. 

Is this likely to be an issue with her Apple ID/iPhone, or is it a VFNZ issue, with the number not connecting to the iMessage servers? 

Quite frustrating