Pakistan requires imported phones to be registered (the PTA/DIRBS system) before they can use local SIMs long-term. Registration duty on a recent flagship iPhone runs well into six figures in rupees, so many imported phones simply never get registered — and after the grace period, local SIMs stop working on them.
Why roaming data is different
Registration checks apply to local Pakistani SIMs. An international roaming eSIM connects your phone as a visitor on a local partner network — the same way a tourist's home SIM roams. That's why a roaming data eSIM works on unlocked, eSIM-capable phones that aren't registered with PTA. It's a fact of how roaming works worldwide, not a trick.
What you should know before buying
It's data-only: no Pakistani number, no SMS — so keep your existing SIM in another phone for bank OTP codes, and use WhatsApp as usual. Check your phone has eSIM hardware (dial *#06# — look for an EID) and is carrier-unlocked. And start with the smallest plan to confirm on your exact phone; a good store refunds you if it can't connect.