My experience so far, and how it can help other new people...
Hello everyone, I've got the s3 a few days ago, and I've got a little bit of story, and maybe some info that can help others who messed up like I did.
Originally got this phone last Sunday, and when I did, I immediately looked into the best roms to get. After watching a few videos on Youtube, I found a site, samsungs3root.com, which had reviews of the best roms out. After I decided on cm10, I followed the instructions on the site for rooting and installing roms.
Unfortunately, due poor formatting, web browser errors, and me not paying attention to what I was doing(mostly this one), I messed with the bootloader of my Sprint phone, by running the Verizon app for unlocking it. When I restarted my phone, It wouldn't come on, it was hard bricked.
I returned the phone(I know, some of you may not agree with this, but I don't care, it's not like they won't fix it and sell it anyway), and got back another Thursday.
Today, I successfully flashed the phone and installed the cm10 rom. Unfortunately, the build i installed was a nightly update, not a stable version. The version I installed had bugs which prevented my camera and google search from working. The best way I could think of fixing this was to revert to stock and start from the beginning. I used odin3 and reverted to stock, but when I had the chance, i put clockworkmod back on. When I got the phone back on, I had no data and was getting the "no sim card" error. I've installed the OTA(Over the Air) updates, and still couldn't get it, and realized the problem may be because I didn't install the updates with stock recovery(if that's the right word, whatever clockworkmod overwrites). I've since reverted to stock again, have NOT put clockworkmod back on, and am in the process of installing the OTA updates to see if I can get the "no sim card" error to go away.
It took about 6 updates and restarts to get Data to come back on, and now I don't have the "no sim card" error. Right now I'm back at stock, testing out data to make sure it works, and finishing installing any OTA updates. If it does come back, I'll reflash with clockworkmod, and then use the most recent build of cm10 and hopefully, my camera will work.
What I learned from this:
Pay attention to what you're doing. If you have a Sprint phone, use only Sprint stuff. There's a reason everyone stresses that stuff.
If you're using a custom rom for the first time, especially if you're new to rooting and flashing, download the latest STABLE version, and only when that works, if you feel like you can handle it, use the newer builds.
If it doesn't work, take a step back. If it still doesn't work, start from scratch.
Anyway, since I've kinda messed up in every way possible, I know a little bit about what I did wrong. The posts in another forum by users Skunkape60 and responsbility helped me get through the "no sim card" error, so props to them for figuring it out.
Anyone with any advice or questions, post below. I'm very much new at this, so I'm learning too, but maybe some seasoned vets can help out, and maybe I can help somehow.
Thanks to this awesome community for helping someone make the jump from iOS to Android.