The night before a flight is the wrong time to discover that your phone is carrier-locked, that your bank sends one-time codes by SMS to a SIM you are about to remove, or that your charger says 220V only and the hotel runs on 120V.
Check the carrier lock before you pay for anything
On an iPhone, open Settings > General > About and scroll to Carrier Lock. If it says “No SIM restrictions”, any local SIM or eSIM will work. Anything else means the handset is still tied to the network that sold it, and no amount of airport shopping fixes that.
On Android the label moves around: Settings > About phone may show “Network unlock” or “SIM lock”, and on Samsung it sometimes appears only under Settings > Connections > SIM manager. A locked phone can still roam on your home tariff, it just cannot adopt a cheap local SIM, which is the whole reason to check first.
For eSIM support, iPhone XS and later (plus the 2020 SE) handle it, as do most Pixel models from the 3a onward and recent Samsung flagships. The install path is Settings > Cellular > Add eSIM on iOS; on Android it sits under Network & internet > SIMs > Add eSIM. Install the travel eSIM at home on Wi-Fi, because activation needs a data connection and the airport captive portal will not provide one.
Data: roaming off, maps downloaded
Switch data roaming off until you actually need it — Cellular > Cellular Data Options on iOS, Network & internet > SIMs on Android. A phone that roams with data on can drain 8 to 12 percent of battery per hour just hunting for a tower, and the bill that follows a background photo sync is genuinely shocking. A 5 GB regional eSIM typically costs $10 to $20 against $8 to $12 per day for home-carrier roaming.
Download maps before leaving. In Google Maps, tap your profile picture, choose Offline maps > Select your own map, and pinch out until the box covers the city. A metro area at default detail lands around 150 to 300 MB, and the download must happen on Wi-Fi. The same applies to Google Translate: offline language packs are 40 to 60 MB each and make menus readable without a signal. The offline maps walkthrough covers the storage side if space is tight.
Power: what flies, what charges, what fries
A 10,000 mAh power bank delivers roughly two full charges to a 4,500 mAh phone once conversion losses are counted, and it has to travel in the cabin, not checked baggage. Most airlines cap lithium batteries at 100 Wh — about 27,000 mAh — with anything between 100 and 160 Wh needing prior approval, which is the rule set out in the IATA dangerous goods regulations.
Read the label on your charger brick before packing it. “Input: 100–240V” means a plug adapter is all you need anywhere in the world. “Input: 220V” means a voltage converter, and a hair dryer or travel kettle rated for Bangladesh’s 220V will run at half power or burn out on a 120V supply in the United States or Japan. Phone chargers are almost always dual-voltage; heating appliances almost never are.
Bangladesh uses 220V with type C, D and G sockets, so a UK-style adapter is the useful one for outbound travel to most of Europe and the Gulf, while the US and Japan need type A. Carry one 65W USB-C charger with two ports rather than three separate bricks; it charges a laptop and a phone overnight from a single socket.
The two-factor trap nobody warns you about
If your bank, work account or email authenticates with an SMS code sent to the number you plan to remove, you will be locked out at the worst possible moment. Fix it before you fly, not after. Move the account to an authenticator app or a passkey, print or store the backup codes somewhere offline, and add a second trusted device.
While you are in there, store an encrypted photo of your passport’s photo page and your travel insurance policy in a password manager — a note app or the camera roll is the first thing a thief checks. Also confirm that your backup method actually completed: a real phone backup is worth more than a screenshot of one.
The thirty minutes that save the trip
- Update the phone and the airline app at home. A 4 GB system update over hotel Wi-Fi at $10 a day is an expensive mistake.
- Free up at least 8 GB for photos and video; check Settings > General > iPhone Storage or Storage on Android.
- Add the boarding pass to Wallet and screenshot the barcode as a fallback — airport Wi-Fi fails at exactly the wrong moment.
- Set alarms for the destination time zone before departure and check that the phone has switched by landing.
- Save the embassy number, the hotel address in the local script, and 3,000–5,000 taka or $50 in cash for the first taxi.
One last item: if you plan to tether a laptop abroad, read using a phone hotspot without burning data before you enable it, because a single Windows update can consume an entire day’s allowance in twenty minutes.