To my knowledge, only Moto uses encryption on the boot loaders. HTC went with a different NAND lock scheme, which has been fully broken now, allowing custom builds/kernels to be flashed. Samsung also has open boot loaders, but their 'security' mechanism is a kooky file system. Regardless, there's several builds available for the GS phones, which include kernels.
I'm not sure about LG, to date, they haven't had an Android phone that's really garnered any significant community interest, so I'm not certain whether or not they use a locked boot loader or not.
Relating to your longer comments on Symbian and multi-tasking, I have not used Symbian so I can only comment on WebOS/Android/iOS. Android is still full multitasking, iOS is not. iOS only allows a relative few applications to run at the same time. Android will allow you to open as many apps as you wish, though the OS will put unused processes to sleep as you open more applications. If you go back to a sleeping process, Android will make it active again. This is why you don't get OOM errors with Android the way you will with WebOS.
I would prefer developers build in a definitive 'Exit' option into their applications, but a developer not doing this is hardly a deficiency on Google or Android.
How is Android full multitasking? You can open as many apps as you wish on iOS too. Your point is that not many things run at the same time. But the same goes for Android. Not all those apps stay actively running in the background.
How many things run at the same time on Android? You can probably get your browser, navigation, and music running. But can't you do the same thing on iOS? The fact is you can't have as many things running as you'd like. IF you open Angry Birds on Android then go to your email as you launch a bird, is that bird going to keep flying? Hell the whole app closes down. Whoopdedoo multitasking my ass. When you open a Youtube video from the Youtube app, can you go read your email and have the audio keep playing? It's not freaking multitasking. And for other apps where there's nothing going on live unless you interact with it, how do you know your app is using saved state versus staying open the whole time? Does it really matter? It seems to matter to you that iOS uses saved states.
The reason it's NOT full multitasking is the OS starts killing stuff off. Only a few things can STAY OPEN at a time. A few examples are like your IM app. Android uses the concept of saved states too, but the minute iOS uses it, you will blast it for not being full multitasking. The fact that the OS starts making decisions for you and closing stuff off tells you that it's not really actively running anymore, and that this isn't full multitasking. Sure it can close it and save some of the state in memory, but is that multitasking? It's pseudo-multitasking. Both OSes do that.
But like I've said before, what Apple has done works, and what Android does works too. It's NOT full blown multitasking. I'm not saying Apple rulez or whatever, but this is not a reason why Android blows iOS out of the water. The multitasking is abysmal on both if you compare to WebOS and Symbian, and this has been my point all along. If you want to say Android is less shitty in multitasking than iOS, then sure so be it, but they're both loads of shitty when compared to a true multitasking OS for the multitasking aspect. Symbian and WebOS operate more like your computer does. When you fire up AIM and the browser and your e-mail, imagine switching between the 3 apps on full screen mode. That's exactly how Symbian and WebOS work. While you can only see 1 and interact with 1 at a time, they're all working. Apple and Android utilize saves states. When you switch out of GTalk, to your email, Google invokes the push notification system just like Apple would when you hit HOME out of your Beejive App. It's not really running anymore. But it works for me, so I'll take it.
What's laughable is that you think that AT&T is a "great cell phone carrier." They are by far the worst carrier in all of the US.
They're not that bad. They rule in speed according to PC World and even the reliability #s they gave for AT&T showed it beating Verizon in many cases except SF and NYC. Furthermore, it's one of the few GSM providers in the US. T-Mobile is another, but it uses even less heard of frequencies. At least I can take my AT&T phone overseas and use it. Similarly, I can receive texts overseas without even doing anything. GSM connections are EVERYWHERE. So yeah, this is the sacrifice I make so I can use SIM cards and swap phones whenever I feel like it to whatever unlocked model I choose.