[Xperia Arc General] caqo71:
OK, since I'm a frecuent user on this forum, but not a dev. I'm starting this thread to solve some doubts from users that wonder about when they can flash or not flash a ROM when their BootLoader (BL) is Locked, or Unlocked.

I'm pretty sure that this answer is in many posts, but this time I'll be clear about just this in detail.

At this moment, I feel the need to write te post un uppercase, because there's a lot of users that don't understand what is the difference of having an Unlocked, or Locked Bootloader because they just don't seach the forum, and even, people that mix the terms bootloader with root, or not rooted phones. As writing in uppercase means yelling, I'll content myself and i'll do it normally.

Facts:

- The bootloader has nothing to do with the rooting regarding to flashing roms

- all Coocked roms, needs an Unlocked bootloader because they need a "different" Kernel to work, but to flash a "different" kernel, you need to have your Bootloader unlocked

- Rooting your phone is just to have acces to the main files of the rom. Phones has an internal, and external memory (SD card), but you can only see the external, so, to have access to internal memory, you need to have your phone rooted. And, some software that makes changes to your android system, needs to acces the internal memory, so, that software asks you to have a rooted phone.

- The ONLY ROMS that can be flashed to a Bootloader locked phone, are all the main roms (ftf), or the roms that don't have any changes regarding to the kernel. They just are roms that don't have any changes regardind to its functionallity. ie: no overclock, or any other behabiour that demands an alternative kernel to work. But, you always have to install ClockWorkMod (CWM) to flash the roms, so, as nomal kernels doesn't have it included, you have to install it from the market, or from an apk. After doing that opperation, you have to install again the CWM to get the ability to flash some more modded things.

- if you have a rooted phone, doesn't mean that you can install all the roms. An nlocked bootloader is mandatory.

- Kernel modules, and Basebands Libs are two sepparated thing. When you flash roms that are for Gingerbread, you must to flash a kernel that is for GB rom, and if you're flashing an ICS rom, you need to flash a kernel that is for ICS rom. After flashing any of the GB or ICS roms, you have to flash corresponding kernel modules, and it should be done after flashing the main rom. If you want to change your BaseBand (BB), you also have to flash the corresponding BB libs. Some people gets confused about Kernel modules, with BaseBands libs, so they generally gets bootloops after flashing the roms.

- Main Baseband, and main roms (Whole FTF file), should be flashed with Flashtools. And baseband libs, and kernel modules, has to be flashed with recovery ClockWorkMod (CWM). IE: if you want to change your BaseBand from 64 to 70, you have to flash the main Baseband file with flashtool (as when you flash a whole ftf rom). Main ftf baseband files are just ftf files to flash with flashtools. This procedure doesn't kill or modify your actual rom, it just change the Baseband... After that opperation, you have to get into recovery (CWM) mode, and flash the corresponding Baseband libs, in this case, you should flash the BB70 libs.

- there are some cases, and from some regions (countries), that with Baseband 70, your SIM card doesn't works, or it's works partially, in that case, you have to flash the ftf file from BAseband 36, and use the BB libs fron te rom. It happens when you flash ICS roms, but ftf baseband 36 works very well with baseband 70 libs. This is just a tip for all those their SIM card doesn't work with BB 70, like me.

- (more to be added)

(This is for developers): As I'm seeing all the time people asking if the rom could be flashed in a locked bootloader, at the other side, I see devs that don't tell if the rom could be falshed in a locked bootloader, so, I'm giving a diana to all the noobs that ask for that.

Don't spam this thread. If you wanna add something, giveme a PM and I'll add to the list.

PS: sorry for my english. I'm spanish LatinAmerica. :)