The short answer: turn roaming ON for your travel eSIM, and keep charges in check on your main line
Here's the bottom line first. For a travel eSIM you use abroad, data roaming should generally be set to "ON." An eSIM works by connecting to a local network to provide data, so if you switch roaming off, the eSIM you just bought won't be able to connect. The line you actually need to worry about for unexpected charges is your regular home line (your main SIM). If you turn both mobile data and data roaming "OFF" on that line, you can largely avoid surprise costs while traveling.
In other words, the trick is to configure each line separately. Keep your main line quiet and let the travel eSIM handle data — once you've got this division of roles down, there's no scrambling once you arrive. We'll walk through the details step by step below, and our setup guide shows the on-screen settings as well. Especially if it's your first time, understanding this one point before you leave makes the whole trip easier.
What is data roaming, and why turn it "ON" for an eSIM?
Data roaming is the mechanism that lets your phone borrow a local carrier's network to get data in places where your own carrier's signal doesn't reach (mainly abroad). It helps to picture it as your phone saying, "My own network isn't here, so I'll use a partner network instead."
Roaming has a reputation for being expensive, and that's because using your regular home line abroad as-is can, depending on your plan, rack up steep international data fees. The problem is that this bad reputation takes over, and people end up switching off roaming on the very eSIM that needs it on — one of the most common reasons travelers find their "eSIM won't connect" overseas.
A destination-specific eSIM plan like Bloomy, by contrast, is priced from the start with local use in mind. Because the eSIM itself relies on a local network, that eSIM line typically only connects once data roaming is turned on. If you assume "roaming is dangerous" and leave it off, things won't work as expected. The key thing to remember is that "roaming on your main line" and "roaming on your eSIM" are two entirely different things. The word is the same, but the first is the risky one and the second is the one you need — keep them separate in your mind.
If this is your first time using an eSIM, it's worth checking whether your device supports eSIM first. You can't add an eSIM to a device that doesn't support it. And if your device still has a SIM lock, adding a line or switching between lines may not work smoothly.
How surprise charges happen — and how to avoid them
Most surprise charges abroad don't come from the eSIM at all. They come from your main line (home SIM) quietly connecting overseas without you realizing it. Things like app auto-updates, photo and data backups to the cloud, background updates in map apps, and automatic email fetching all keep communicating even when you're not touching the screen. If that traffic runs over your main line's roaming, you end up with the classic "I didn't even use it and still got charged" situation.
The fix is simple: turn off mobile data and data roaming on your main line, and let only the travel eSIM handle data. Splitting the roles line by line, as in the table below, makes it easy to keep straight.
| Line | Mobile data | Data roaming | Role |
|---|---|---|---|
| Travel eSIM (Bloomy) | On | On | Handles data while abroad |
| Main line (home SIM) | Off | Off | Prevents unintended overseas charges |
If you want to keep receiving calls to your home number, you can leave the main line itself on and turn off only "mobile data" and "data roaming" (note that fees for the calls themselves — incoming and outgoing — depend on your plan). Because how charges are handled varies by your main line's contract (as of June 2026), if you're unsure how your main line behaves abroad, it's worth checking your carrier's latest guidance too. Confirming this once makes it easier to decide whether to switch the main line off entirely or keep just the number active.
How to set it up on iPhone and Android (managing each line)
Menu names differ slightly by device and OS version, but the idea is the same. Remember "keep the main line quiet, let the eSIM handle data" and you won't get lost even if the wording on your screen is a little different.
On iPhone
- Open "Settings" → "Cellular" (or "Mobile Data").
- Select your travel eSIM line, then turn on "Turn On This Line" and "Data Roaming."
- Under "Cellular Data," switch the line used for data to your travel eSIM.
- Select your main line, turn off "Data Roaming," and turn off the line itself if needed.
On Android
- Open "Settings" → "Network & internet" → "SIMs."
- Select your travel eSIM, turn the SIM on, and turn on "Roaming."
- Set the SIM used for "Mobile data" to your travel eSIM.
- Turn off "Roaming" on your main SIM (the label varies by manufacturer).
You can find the detailed flow for each device, matched to its screens, in our setup guide. As for timing, a reliable approach is to just install the eSIM before you leave and activate the line after you arrive. That said, activation timing can differ from plan to plan, so please check the details before purchasing. If a setting doesn't take effect right away, toggling airplane mode on and off or restarting your device often helps the line switch over.
Choosing data amount and duration (a rough guide when you're unsure)
Along with roaming settings, another common point of hesitation is how much data and how many days to choose. With data roaming on, you'll be using maps, search, social apps, and messaging apps locally, so it helps to picture roughly "what I use and how much" before you leave.
- Mostly maps, chat, and quick lookups: a relatively small amount of data is often enough as a rough guide.
- Sharing photos and videos, or using maps for long stretches: it's reassuring to have some extra headroom.
- Heavy video streaming, video calls, or tethering: a large-capacity or unlimited plan may be worth considering.
These are rough estimates that shift depending on how you use your phone (please check the latest figures on the comparison page at the time you buy). Note that whether tethering (sharing to other devices) is allowed varies by plan, so if you want to use a laptop or tablet too, it's worth checking the conditions before purchasing. Even with an unlimited plan, conditions such as the number of usage days, speed management, a fair use policy, and tethering availability may be set depending on the plan and the country or region, so we recommend confirming these in advance. For long stays or study abroad, choosing a plan with more days and data headroom than a short trip tends to be a better fit. You can compare specific prices and data amounts by country, data volume, and length of stay on the eSIM comparison page.
What to check first when you've set it up but still can't connect
If you've turned roaming on and still can't connect, going through the following in order makes it easier to pin down the cause. Rather than anxiously redoing your settings, checking one item at a time often resolves things faster.
- Is data roaming really turned on on the travel eSIM line?
- Is the line used for "mobile data" still set to your main line by mistake?
- Have you tried toggling airplane mode, or restarting the device?
- Have you arrived and are you somewhere you can actually receive a signal? (Before arrival, in flight, or underground you may be out of coverage.)
- Has the plan's start date or activation time already passed?
- Is "Network selection" set to automatic? (Leaving it on manual can make connecting harder.)
If that still doesn't help, our connection troubleshooting page has step-by-step fixes by situation. Skimming it before you leave saves you from scrambling on the ground. Connection quality varies with the local network, area, and time-of-day congestion, so sometimes simply stepping outside a building or moving a short distance is enough to improve things.
A checklist for before departure and after arrival
So you're not second-guessing things on the day, it helps to split tasks by timing. Before you leave, it's best to handle everything at home where you have Wi-Fi.
Before departure (on home Wi-Fi)
- Install the eSIM on your device.
- Set data roaming on your main line to off.
- Double-check that your device supports eSIM.
- Pick a plan with the data and duration you need.
After you arrive
- Turn on the travel eSIM line and its data roaming.
- Switch the line used for data to the travel eSIM.
- Confirm you can connect in a map app or browser.
- If it won't connect, try toggling airplane mode or restarting.
An honest note about using Bloomy
Bloomy plans are generally data-only. Once data roaming is on you can use the internet, but voice calls and SMS (text messages) on your home phone number won't work as-is. If you need a phone number or SMS verification, please look into other options too — for example, configuring your main line to "keep just the number active," or using a local SIM or a plan that includes a number alongside it. App-based calling and messaging such as WhatsApp can often be used wherever you have a working data connection.
If you're unsure about your destination or how much data you need, you can search for a plan by country, data volume, and length of stay from the eSIM comparison page. You can review your purchase from My Account. If you'd like to brush up on eSIM basics, the eSIM guide is there to help. Bloomy is set up so that first-time users can follow everything from the setup flow to connection checks without getting lost before or after buying. Connection quality can vary depending on the local network, your device, and the area.
Frequently asked questions
You can find answers to more detailed questions on our FAQ page. Use the FAQs below as a reference too, so you're not caught off guard once you arrive.
