Suspend the line first, don't panic
The first thing to do after losing a SIM is suspend the line to prevent misuse. From there, choosing a replacement method, getting the new SIM, and activating it restores your same number.
If the phone itself is missing, try locating it first
If you've lost the whole device along with the SIM, it's worth trying to locate it before requesting a replacement SIM.
Frequently Asked Questions
Does my phone number change when I replace my SIM?
No -- replacing a SIM issues a new physical chip for the same number, so your phone number stays exactly the same.
My SIM is damaged and I can't make calls while waiting for a new one -- what can I do?
Visiting a store in person usually gets you an immediate replacement, so that's the fastest option if you need to make calls urgently.