📶 eSIM, roaming or local SIM — staying connected abroad

1. First: can your phone even use an eSIM?

An eSIM is a SIM built into the phone that you activate with a QR code — no physical card. Most phones from the iPhone XS onward and recent flagship Androids (Pixel, Samsung) support it, but the phone must also be carrier-unlocked. Some older or mainland-China-market phones have eSIM disabled.

• ✓iPhone: Settings → General → About — look for a Digital SIM / EID entry
• ✓Android: Settings → Network → SIMs → “Add eSIM” (wording varies by brand)
• ✓Unsure? Dial *#06# — an EID number means the eSIM hardware is there
• ✓Your HK physical SIM stays in the phone; the eSIM runs alongside it (dual SIM)

2. Roaming vs travel eSIM vs local SIM

• ✓Roaming (your HK carrier abroad): zero setup and keeps your number, but day-passes run ~HK$88–168/day — only worth it for a 1–3 day trip
• ✓Travel eSIM (Airalo, Nomad, Saily, Ubigi…): cheapest data, installed before you fly, and your HK number stays reachable for calls and SMS on the side. Best for most trips
• ✓Local physical SIM (bought on arrival): often the very cheapest with the most data, but you swap out your HK SIM and may have to queue and show a passport

3. Set it up before you fly

Install and activate the eSIM at home on Wi-Fi — the QR code often scans only once, and while some plans start their clock at install, others start at first connection abroad, so check which.

• ✓Install on home Wi-Fi and label the eSIM (e.g. “Japan”)
• ✓Set the eSIM as your data line; keep the HK SIM as the voice/SMS line
• ✓Turn OFF data roaming on the HK SIM so it never silently racks up charges
• ✓Only enable “allow data switching” if you want the HK SIM as paid backup data

4. Keep your HK number alive for OTPs

The single biggest trap: banks, Octopus and logins text a one-time code to your HK number, and a data-only eSIM can't receive those. Keep the HK SIM active (voice/SMS on, data roaming off) so 2FA still works — receiving an SMS on a HK number abroad is usually free.

5. The gotchas that catch people

• ✓“Unlimited” plans throttle hard after a fair-use cap (often 1–2 GB/day) — read the small print
• ✓Hotspot / tethering is blocked or capped on some eSIMs, which matters if you share to a laptop
• ✓Mainland China: Google, WhatsApp and Instagram are blocked — an eSIM routed via Hong Kong/overseas, or one that says it “bypasses the firewall”, saves needing a VPN
• ✓Some countries require passport registration for a local SIM (Thailand, Vietnam and others) — eSIMs skip this
• ✓Regional plans (“Asia”, “Europe”) cover many countries on one eSIM — handy for multi-country trips