iMessage and FaceTime not working

[BrianBo_2945118]

Ok so I ported over from O2, on a eSIM, to Smarty with a physical sim. The swap occurred yesterday on schedule. However, iMessage and FaceTime only work with my iCloud email, and in the iPhone 13 settings, my number isn’t visible. Just updated now to new iOS, and no change. In my iCloud settings it says “This phone number cannot be used by iMessage and FaceTime. You must have a sim associated with an Apple device for (my number) to be used for imessage and FaceTime “

I’ve tried all the resets, sliding toggle switches, network setting etc. and no further forward. 
there is no seating in Phone to add the number, it’s only in iCloud, and the above message appears ⬆️

also, WiFi calling has disappeared (before iOS update)

[RovingRaspberry]

I had this problem recently, when briefly trying GiffGaff

A visit to my local apple store and a call from their tech support didnt solve the issue.

So, I contacted Voxi, as that's who my main number is currently with.

This was  the bizarre fix, which worked and fixed the issue :

1, Turn off both iMessage and FaceTime

2, Set up a NEW contact, as follows :

First name : My Card 

Last Name : NEW

Phone Number : Your own number, in international format, +44 7xxx xxx xxx

NOTE the capitalisation in the name : My Card NEW

Dont forget to save the new contact

3, Turn off your iPhone

4, Turn on your iPhone

5, Turn on both iMessage and FaceTime

Cant believe it solved this issue for me, but it did

[SmartyTrousers]

You mention you can't see a setting for you to enter your phone number. In iOS 18 you can find this at Settings > Apps > Phone > My Number. If it won't let you save the number you enter, I would suggest trying again in a day or two.

I think the message you are seeing in the iCloud settings simply means it doesn't think your phone is currently using a SIM which matches the phone number on your iCloud account, hence needing to enter the number as described above, or possibly wait for a background SIM update then trying again, if the number won't initially save.