[System Settings] Display device phone number in About panel

Setting as incomplete from the settings side, that's not in the current design:
https://wiki.ubuntu.com/AboutThisDevice#Phone

Perhaps this should be in the Phone settings, rather than the "About This Device" settings.
<https://wiki.ubuntu.com/PhoneApp>

I've made a request for user research on where people would expect to find this -- in "About this phone", in "Phone" settings, in "Cellular" settings, in the Contacts app, or somewhere else.

That shouldn't stop anyone from implementing it: being in any of those places would be better than none at all. Remember that the presentation would need to differ for single SIM vs. dual SIM: in single SIM it could be a single “Phone number" item, whereas in dual SIM it would be a "Phone number:" section with items for each SIM.

Just a brief comment, a subscription's phone number is often not stored on the SIM card (it's optional according to [1] and many operators just don't fill it). Also, there can be more than one phone number assigned even to one card (but showing the first/primary one should be fine).

[1] 3GPP TS 31.102 "Characteristics of the Universal Subscriber Identity Module (USIM) application", section 4.2.26 "EF_MSISDN"

Added to the about page, track dual sim mods separately

Works fine with mako HW, image 138, Orange (UK) SIM card.

It doesn't show on krillin with 1 SIM, I guess that's why Jonas reopened it?

The research I requested in May has just been completed. It turns out that most people look first in the Contacts or the "Phone" settings, not in "About This Phone". That shouldn't stop you from fixing flaky presence in Krillin or whatever, but meanwhile I've reported bug 1364452 on moving it.