LINE App centers messages and Internet calls on a LINE account rather than the phone’s ordinary SMS archive. Conversations can continue on a main phone and selected companion devices, but the account, its chat history, and its device roles need deliberate setup. Reinstalling or registering again is not the same action as signing back into an intact account.
Main device rules
LINE App treats the device used to establish the account as the main device. That phone manages the number, email address, password, account transfer, chat backup, and Letter Sealing settings. A computer, tablet, or another supported device can sign in as a sub device after the main device turns on Allow login.
Sub devices do not duplicate every account control. They cannot transfer the account, create the chat backup, change protected account details, or buy stickers and emoji. An iPhone can act as a main device but not as a sub device. These distinctions matter when someone expects a second phone to behave like a mirrored copy of the first.
Creating a new account with a phone number, Apple ID, or Google account that already belongs to another main device can automatically delete the previous LINE account. A deleted account cannot be restored. The safe choice on replacement hardware is the account-transfer path, not new registration with familiar identity details.
History needs preparation
Moving LINE App between phones requires more than entering a password. For a move within the same operating system, the old device should back up its chats to iCloud Drive or Google Drive. The cloud account needs enough free space, and the backup needs a stable connection. After the backup completes, the user can transfer the account through the supported transfer flow.
A move between different operating systems has a stricter boundary. A backup PIN can carry the latest fourteen days of chat history, but older history in iCloud Drive or Google Drive cannot cross that operating-system boundary. Without a backup PIN, a cross-platform move transfers no chat history. If the old device is unavailable and neither a cloud backup nor a PIN exists, LINE App cannot reconstruct the missing conversations.
Delete or unsend
Delete and Unsend affect different copies of a message. Delete removes an item from the user’s own screen and leaves it visible to recipients. Unsend removes content sent by that user from both sides, subject to the applicable time limit. Deleting first closes the second option because deleted content cannot then be unsent.
Unsend also cannot erase what someone already read in a notification preview. Standard use leaves a notice in the conversation after removal. Some regions and memberships have different time limits or a discreet option for unread content, so a label that appears on one account may not exist on another. LINE App therefore should not be treated as a guaranteed recall system.
Calls and continuity
Messages and voice calls use the account across supported signed-in devices. The companion-device model is useful at a desk, but account recovery and backup remain tied to the main-device rules. A computer session cannot replace a missing phone backup or perform an account transfer by itself.
Before changing phones, the practical sequence is to confirm the registered identity details, create the chat backup, set the backup PIN, and then start the transfer. Skipping those preparations can preserve the account while losing part or all of its local history, especially when the new phone uses a different operating system.
