⚠️ I am not responsible for the content of the links, it is not my content. I have only collected what's still around in the web (or archived). Use a translator if needed.

MobileFree ru as "the goto" forum/wiki
https://justdanpo.ru/data/projects/gsm/ (used to be justdanpo.cheb.ru/) and
https://justdanpo.ru/data/support/elfpack/ elfpack builds

https://github.com/farid1991/patch-se
https://github.com/farid1991/new-patch-se
https://github.com/farid1991/seftool - flash & patch CID29,36,49,50,51,52,53 + Upload file(s) or folder to FS with CLI
https://github.com/Androxyde/Flashtool

http://setool.sonyericsson.org/ ← There are other free tools for basic tasks, use them first.

#Omnius is now free, request account on discord (see "Communities")
https://www.omnius-server.com:9999/ or https://www.kaijousuru.com:9999/
https://archives.omnius-server.com:9999/ or https://archives.kaijousuru.com:9999/

https://multi-com.eu/,browse,id_gr,248,key,service-unlock-devices.html consider buying a flash box, e.g. on multi-com.eu (no affiliate)

https://www.akshayy.com/sonyericsson/index/
https://lpcwiki.miraheze.org/wiki/Sony_Ericsson
https://operationse.github.io/ from sharko and its Github
Wikipedia list of all SE accessories

Telegram channel 'ModdingLikeIts2009'
https://t.me/chomikujpwn request any file from chomikuj.pl (polish file hoster)

Kaijousuru on discord: https://kaijousuru.com/discord
Kaijousuru discord invite link: https://discord.gg/M64MVqeCBe
Kaijousuru is Omnius community: https://www.reddit.com/r/vintagemobilephones/comments/1e36wbe/new_owner_of_omnius_free_firmware_archives/

https://vk.com/se_community
Vintage Phones Archive on Facebook
Xperia Play Discord Server

https://mobilefree.justdanpo.ru/ (also shortly under supertrubka.org, which was originally mobilefree.ru)
https://sony.yt/forum/294-tutorials/
https://www.esato.com/board/viewtopic.php?topic=189669
https://forum.se4ever.ru/
https://se-tuning.cz/
http://www.sonyericsson-world.com/
https://seclub.org/forum/topics/76/
https://www.faq4mobiles.de/foren/sony-ericsson.42/
https://all4phones.de/forum/
https://www.topsony.com/forum/cmps_index.php
https://my-se.ucoz.net/forum/58-124-1
https://mobile-files.com/

Reddit:
https://www.reddit.com/r/vintagemobilephones/
https://www.reddit.com/r/J2MEgaming/

Note: All archive.org timestamps are rather randomly picked. Pages might not be usable anymore.
http://web.archive.org/web/20061128001225/http://developer.sonyericsson.com/site/global/docstools/java/p_java.jsp
https://web.archive.org/web/20101128102447/http://se-developers.net/index.php
https://web.archive.org/web/20120205064356/http://www.se-world.info/index.html
se-nse.net v5 forums
#note: play with timestamps for archive snapshots of se-nse.net
se-nse.net v6 forums
https://web.archive.org/web/20130827151905/http://forum.elfse.com/
https://web.archive.org/web/20120621233459/http://www.se-lifestyle.com/index.php
https://web.archive.org/web/20160625233809/https://forum.se-zone.ru/viewtopic.php?t=3925
https://web.archive.org/web/20111007085513/http://topse.ru/forum/
Developer-se.pl
https://web.archive.org/web/20161017202304/http://secool.ru/
https://web.archive.org/web/20100611210125/http://www.se-stuff.net/
https://web.archive.org/web/20110716043323/http://www.seusers.com/foro/forum.php
https://web.archive.org/web/20100609123842/http://www.c902.eu/
https://web.archive.org/web/20040610190507/http://mobile.box.sk/manufacturer.php3?newsprj=ericsson
https://web.archive.org/web/20060722063621/http://lasyk.net/ https://web.archive.org/web/20100507042749/http://seusdb.10001mb.com/index.php
https://web.archive.org/web/20100421115013/http://semcblog.com/applications/

Vintage Phones Archive with archived SETool files
another SETool archive
another SETool archive
https://chomikuj.pl/GSM-BOX/Sony+Ericsson
https://www.iprotebe.cz/sony-ericsson-section1.html
iprotebe.cz files: https://drive.proton.me/urls/AQ1358PNAR#m27WWE7EV2XJ
https://firmware.center/firmware/Sony-Ericsson/
Dumbphone Repo: https://mega.nz/folder/2aoVnJJJ#ovZJG4cbvIOqLVEJBHrQSQ
https://mega.nz/folder/MtV0HIiB#68pyinmvk9UHpZB6gbF3yQ
TopSony files: https://drive.proton.me/urls/BDTEBARJGW#3fXzAPn6lS1O
archive.org TopSony FWs https://archive.org/details/topsony_firmwares
and https://archive.org/details/tems_20250222
[TEMS topsony archive.org]https://archive.org/download/tems_20250222
Farids 4shared: https://www.4shared.com/u/9KEsFT8x/farid.html
DB3350 stuff: https://disk.yandex.ru/d/SOeLDFdbP1ZuUA
https://www.4shared.com/account/dir/tB2YurBu#dir=kseGk9Pi
https://www.4shared.com/folder/eI_ZJYC9
https://www.4shared.com/u/wCBqbkTu/adhitya_1978.html
unsorted files: https://mega.nz/file/E6pyCIbR#trOMFmCYJVuhcQgahQJGVhq3wGAZPJ43SLJKPoFXRBw

LGTOOL 1.99 & SGTOOL 1.027 .rar

https://archive.org/details/mobile_forums_dump

https://rutracker.org/forum/viewtopic.php?t=3335160
https://rutracker.org/forum/viewtopic.php?t=2276848

https://j2me-docs.narod.ru/ J2me SDK
https://github.com/MIDletPascal MIDletPascal / AMPAS IDE
https://github.com/hstsethi/awesome-j2me collection / list for J2me
https://github.com/hstsethi/j2me-preservation collection / preservation for J2me

https://habr.com/ru/articles/814855/ interpreters for J2ME
https://annimon.com/forum/id261807-0 download MobileBasic 1.9.1
https://nnproject.cc/mp/ Telegram for J2ME
https://github.com/gtrxAC/discord-j2me Discord client for J2ME
https://planet-surfeu.de/programme.php

List of J2me emulators
List of emulators on J2me

https://www.mgmaps.com/download.php
https://wiki.openstreetmap.org/wiki/Trekbuddy
https://vlkgps.sourceforge.net/

http://dedomil.net/games/
https://mobile.phoneky.com/games/
https://www.mobygames.com/platform/j2me/
https://www.myabandonware.com/browse/platform/j2me/
https://bluemaxima.org/kahvibreak/
…
https://archive.org/details/j2me-archive-unified-2019-09
https://archive.org/details/mobiles24j2me and also search archive.org for j2me or jar games
…and many more

https://3dcinetv.com/3d-retro-gaming-in-the-sony-ericsson-w550-blender-i-o/
https://nikita36078.github.io/J2ME_Docs/ J2ME docs
https://docs.oracle.com/javame/developer/developer.html Oracle docs
http://j2megame.atw.hu/
https://billday.com/javame/ list of books
https://sourceforge.net/projects/isoj2me/ | isometric engine
https://j2me.fandom.com/wiki/Tutorials
https://www.wideskills.com/j2me-tutorial
https://bora.uib.no/bora-xmlui/handle/1956/1463 J2me programming MA thesis 2004 […] there are tons of J2me (game) programming tutorials out there, just search

https://www.maxbhi.com
https://n-tel.eu/index.php?id_category=14&controller=category&id_lang=1 (Poland only)
https://gsm-hurt.pl/36-czesci-zamienne-gsm

FAR Manager and its plugins:
https://github.com/d4rkmen/PhoneFS

XS++ source code: https://svn.assembla.com/svn/XS_xPlatform/

http://web.archive.org/web/20070219032816/http://www.davinciteam.com/index.php?page=manual-cablemod
T28 Service and Data Cable Conversion
https://vonkonow.com/using-a-sony-ericsson-dock-as-an-usb2serial-adapter/ DSS-20 as serial for T28 connector
https://isaleksey.blogspot.com/2013/06/usb-rs232-5v3v-semc-dss-20-sony-ericsson.html
T28 connector and info on lpcwiki
MW600 disassembly
- mod/solder MPS-Series speaker fastport to USB-A+3.5mm (✅ done) (or even USB-C with analog audio?)

Sony Ericsson All device Service Manuals (569 files, 8.51GB): https://mega.nz/folder/XZMzSJiR#X2zpiqp11d7MBfMFbuZAcg

https://www.mobilephone-manualsonline.com/sony-xperia/sony-ericsson-pdf-schematics-and-service-manuals/
#TODO upload schematics of : C901, W995, C905, K800/K750
Ericsson GM47/GM48 datasheet: https://www.farnell.com/datasheets/51837.pdf

https://hackaday.io/project/7496-mmr-70-cheap-radio-module
https://hackaday.com/2014/11/12/2-fm-transmitter-for-rasberry-pi/ info summary with FMBerry
https://www.mikrocontroller.net/topic/252124
http://achilikin.blogspot.com/2013/06/sony-ericsson-mmr-70-transmitter-led.html
http://achilikin.blogspot.com/2014/06/sony-ericsson-mmr-70-modding-extreme.html
http://www.elektronik-labor.de/AVR/MMR70_2.html

https://www.mikrocontroller.net/topic/358873
http://tiny.systems/categorie/hardwareHacks/index.html

http://sonyericsson.org:64/ Youtube 2009 with its settings
http://yt2009.wunderwungiel.pl (another YT2009 instance)
http://str.wunderwungiel.pl: simple translation
https://github.com/firetech/Remote-100 Sony Ericsson Car-100 Android Bluetooth App
https://scribd.com/document/395588589/Sony-Ericsson-Secret-Codes
https://www.sony-asia.com/support/resources/en_AP/html/Compatibility/MemoryStick/Mobile_Phone.htm
https://people.osmocom.org/fixeria/talks/
https://github.com/dfrws/dfrws2010-challenge
http://146.59.80.3/ jar benchmarks and file host to transfer files to dumb phone
https://www.youtube.com/@SonyEricssonHub
https://harshalkutkar.wordpress.com/2010/01/20/sony-ericsson-phone-modding-and-flashing-tutorial/
https://mtronicscell.blogspot.com/search/label/Sony%20Ericsson%20Flash%20Files + Guides
https://web.archive.org/web/20080304133859/http://www.akshayy.com/asm/
https://www.mcrf.ru/forum/showthread.php?t=1032
https://romphonix.github.io/

https://archive.org/details/clean-flash-installer
See if you can find whatever you are looking for here:
https://archive.org/search?query=subject%3A%22Sony-Ericsson%22
like https://archive.org/details/se-themes-creator-41626 (there is newer version 5)
https://archive.org/details/Twister_Mobile_Phone_Flashing_Box