Transfer LINE account from a phone to another without losing friends and chat history LINE is a messaging/call application.

I bought a new Android phone, and want to transfer LINE friends, chat history, call logs, groups, groups chat history, from my former Android phone.

How to do?
Warning: LINE only allows one active phone, and will destroy data on the old phone as soon as you log in on the new phone, so be sure to correctly perform this procedure BEFORE logging in on the new phone.
Fast procedure (requires rooted phones)

If you don't remember your LINE PIN code, now is the last chance to change it, LINE will ask for it after you switch. Even if you never set one, it will ask you so better set it now.
Make sure Letter Sealing is disabled in Line settings on your old phone (you can re-enable it after this is complete).
Root both of your Android phones, old and new (absolutely required)
Install Titanium Backup (free) on both phones.
On the old phone, make sure LINE is not running, launch Titanium backup, and backup LINE (App+Data).
Copy the Titanium Backup folder (typically /sdcard/TitaniumBackup/) from your old phone to your new phone. It should contain 3 files or so.
On the new phone, install LINE (don't start it yet), launch Titanium Backup and use it to restore LINE (App+Data). Press &quot;Done&quot;, do not start it yet.
On the new phone, install Root Browser, and use it to copy /data/data/jp.naver.line.android/databases/naver_line to your /sdcard/, then transfer it to a desktop computer (via ADB or email)
Open this file in SQLiteBrowser, go to the Execute SQL tab.
Type delete from setting; then press the Execute button. Click &quot;Write changes&quot; then exit, and copy the modified file back to /data/data/jp.naver.line.android/databases/naver_line
Start LINE on the new phone and log in. When Line asks you about restoring the chat history; say no. Even though Line warns you about loosing your chat history, just go head; all of your data will be just like you left it.

This restores your friends, chat history, call logs, groups, groups chat history.
Note about Letter Sealing: if you forgot to disable it in step 1, new incoming messages will show up as an error and you won't be able to send messages. To fix this problem, just:

Disable Letter Sealing.
Use Root Browser to remove all files that start with &quot;e2ee&quot; in /data/data/jp.naver.line.android/databases.
Re-enable letter sealing.

Thanks to TechGravy for the procedure.
Thanks to YandereSan for the Letter Sealing fix.
Slow procedure (no rooting needed)
If you are unlucky enough to have a phone that can't be rooted (the old one or the new one or both), then your only option is this:

One-by-one for each chat conversation, go to the conversation settings and backup it (Backup all) to the SD card (or email if you prefer).
Move the resulting files to the new phone in a folder called /sdcard/LINE_Backup.
Log into LINE on your new phone. This will destroy all history from your old phone, so only do it when all conversations have been backed up.
For each of your friends, go to the conversation, chat settings, and tap Import chat history, confirm.

In total this will take about 1 minute per friend if you are fast, for instance about 3 hours if you have 200 friends.
Warning: Groups chat history can not be restored by this procedure. This only restores friends, chat history, call logs, groups. Also, it loses any media older than a couple of weeks.