落地后的头 24 小时，按这个顺序来

Install at home on good Wi-Fi, because installation itself needs an internet connection. Waiting until you arrive with no connection puts you in a loop with no exit. When to activate depends on how the plan counts its validity: if it starts on first connection, installing early costs you nothing.

Give it two or three minutes, then toggle airplane mode once. If ten minutes pass with no signal at all, try selecting a network manually from the list, which resolves it often in a crowded airport. What you should not do in that window is delete the profile, because that step cannot be undone.

Not if you installed and tested the profile before flying. A better backup is the material you downloaded for offline use, plus knowing how to reach support without your own data — over airport Wi-Fi, for instance. That is faster than joining a queue to buy something new while exhausted.

You can, but make it a deliberate choice. With data roaming on, the phone may pull data over the home SIM without you asking, and the charges follow that operator's rates. Many people take the middle route: data roaming off, calls and SMS left on. Check the rates with your own operator before deciding.

Do not judge from one day. The first is usually inflated by navigation and updates. Look again after day two. If it is still high, the two fastest adjustments are downloading area maps in advance over Wi-Fi and avoiding video away from the accommodation. If the projection says you will genuinely fall short, arrange more before you run out rather than after.

You can, but many plans start counting at first network attach, so activating at home can waste days. Check that plan's trigger first.

No. Turning off data and roaming for that line is enough, so you can still receive calls and SMS codes.