可以一次买好几个套餐吗？

Yes. Each plan is a separate profile on the phone, and you choose which one carries data at any given time, rather than all of them working simultaneously.

No, they do not pool. Each profile has its own data completely separately. Data is only used from whichever profile is set as the active data line at that moment.

It varies by model and operating system, with no single fixed number for every phone. Check your device manufacturer's own information or use a device-checking tool before planning.

You will need to delete an old, unused profile first. Choose one whose data has run out or expired, and confirm before deleting, since deletion normally cannot be undone.

Switching the data line itself does not use meaningfully more data. But switching too frequently can mean the phone spends time searching for a new network each time, which drains battery more than data.

Normally yes, through your primary SIM as before, since most travel plans are data-only with no phone number of their own. It is worth checking your messaging apps are tied to the correct line though.

It is worth renaming right after installing each one, because once several profiles exist together, the automatic system names are often hard to tell apart and make it easy to switch to the wrong profile.

You can install as many as your device has room for, but activating several at once is a different matter: how many profiles can be live simultaneously depends on the model, and on many phones that number is small. In any case, data flows through only the one profile you have assigned it to. So there is rarely a reason to have several enabled at once — keeping only the one in use switched on makes it easier to verify and harder to spend data from the wrong plan.

Not necessarily — it depends on whether the regional plan's country list covers everywhere you are going. If your route includes one or two countries the regional plan omits, buying a country plan for exactly those gaps is the most precise answer. If the regional plan already covers them all, the extra purchase is paying twice for the same coverage. The check is to open that regional plan's country list and compare it against your itinerary country by country before you buy.

The fix is to delete a profile that has expired or been fully used to free a slot, but be certain it is finished with, because deletion is usually permanent and many plans cannot be reinstalled with the same code. The better answer is to plan the count before departure. If you need more plans than the device can hold, look at a regional plan covering several countries in one profile, or schedule the later installs for a point in the trip where you will have accommodation Wi-Fi.

Technically no — each profile works independently. But buying from one place has a practical advantage: when something goes wrong you have a single point of contact and every order in one place, rather than working out which plan came from where while abroad with limited time. If you do buy from several sources, write down before you leave which plan came from whom and how to reach them.

Look in the phone's mobile network settings, where there is a section naming which profile is assigned to carry data. The exact location and wording vary by manufacturer and OS version, so look for a heading about mobile data or cellular plans. Watching the network name in the status bar helps too. If you named the profiles clearly at the start, reading the answer off the settings screen takes seconds.