Comment 10 for bug 1450255

I specced that the SIM ID include the phone number if there is one, otherwise the IMSI. <https://wiki.ubuntu.com/Networking#sim-id>

However, some of the current display points for the SIM ID may not have enough space to do that, particularly the switcher in the Phone and Messages apps. <https://goo.gl/vn5wY6>

Using the carrier would work as long as your SIMs are from different carriers. I don't know how often that's true.