okay so I just want to add my two cents into this conversation lol.
iRizwan there are a lot of factors about your claimed ability to unlock via hardware and server that I just find very hard to believe. I'm not trying to like call you out or anything but I just would like to point out some key areas about what I've read in this thread that i feel everybody needs to know about to remove any confusion on the topic.
I'm going to separate everything I know into the following categories, and then individualize a set of subcategories for each category. Ipads will sub into WIFI and CELLULAR, and iPhones will sub into HARDWARE and SOFTWARE.
IPAD
WIFI
WiFi only iPads can ONLY be removed via Apple's Servers. No two ways about it. I unlock dozens of these things weekly. You have to know somebody who either works at Apple and has access to GSX, know somebody who has hacked GSX and gained access, or hacked GSX yourself and you have access. Unlocking ANYTHING by just the Serial Number only proves this theory 1000 times over. Hacking GSX is not something that is likely to happen, its a part of Apple's Internal Suite of tools and operations. If by chance you happen to get your hands on a login, chances are its either fake, burned, or soon to be burned. Not every employee with access to GSX has the same power. Some are only allowed to do very little, while others are able to do whatever they want. Suppose you got your hands on one of these admin accounts? Still not going to happen like you think. GSX logins will only allow access via very specific and predetermined IP addresses (they also check things like MAC address, geolocation, OS being used, your computers username, your hard drive serial number, and Im sure much more). Okay, so say you have all of that taken care of, you should be good right? Wrong. They also only allow logins to be accessed from certain times of day. So say you know what time they guy works? Well then you better make sure he's not logged in at the same time that you try to use it to log in (but if it only works during the hours he's at work guarantee that he's logged in and using it) otherwise they will instantly reject and permaban that account and personally investigate why bossman's account has been compromised. Wifi only models cannot be done via hardware.
CELLULAR
Any iPad with a SIM card (sans the iPad Pro because its not like they're not hip to this by now) can be bypassed via hardware method. iRizwan you mention that it takes superior skills and tools? I would have to disagree, this information is all readily available online in multiple places, a single google search for "iCloud bypass iPad mini hardware method" will return more than enough information for somebody to figure it out. There are even hundreds of videos on youtube that show exactly how to do it. As for tools, until recently I have been ridiculously lacking in this department. My weapon of choice for this method was a hair dryer I hijacked from my girlfriend, a couple guitar picks I had laying around, and a sturdy safety pin. Dozens of iPads completed. You are misinformed about the iPad Air 2's and later models losing both WiFI and Cellular data. You are correct in that bypassing iCloud on these models will lose the Cellular functionality though. This is because every single iDevice has a self generated Serial Number that is based off of multiple internal components such as: WiFi MAC address, IMEI, baseband serial number, and a few other components I know that I'm forgetting. When you remove the parts mentioned in these guides (I will be posting detailed guides eventually for all these devices on here for everybody to enjoy) it breaks the SIM functionality of the device. With the IMEI and baseband no longer being a part of the algorithm that generates the devices serial number, it is forced into DFU mode to then generate a NEW and totally unique serial number because no other wifi only iPad is going to have matching MAC address, bluetooth, etc. With a new serial number there is not going to be an iCloud account attached to it, so when you restore the device with the matching wifi only ipsw it becomes a brand new device. Caveats of this are having to tear apart the device which can cause damage, screen breakage (or worse, LCD breakage). For the later models such as Air and Air 2 it DOES break the WiFi as well due to how the device is made, BUT now that there is a jailbreak for all the way up to 9.3.3 all you have to do is jailbreak the device and install the correct Cydia package and the WiFi will be restored. For the iPad Mini's and I believe Air and Air 2 when you remove the resistor your job is not over. You have to then either replace the resistor into another spot, or somehow create a short in place where the resistor would go. Otherwise if you just remove the resistor the device will see itself as either an iPhone or an Apple TV. If you just try to have iTunes restore it with whatever firmware it thinks the device is it will not work.
IPHONE
HARDWARE
There are NO hardware methods like the one used for iPads that can be applied to any iPhone. Period. iPhones more than likely have the same resistors that can be removed and disable the SIM functionality, but you would be stuck with a permanently bricked iPod (if the device even thinks its an iPod at that point). Just like with the iPads where the device will see itself as a different device, it will be stuck in this state, unable to restore because there is no matching firmware to restore over the top of it. You would not be able to just pick an iPod ipsw and flash it over the iPhone(iPod) because of the same reason that the iPad(Apple TV) would not restore with an Apple TV ipsw, there are too many checks that would not pass nor are the iBoot, iBEC, or iBSS the same. The ONLY way of doing any type of hardware bypass would be to physically remove the NAND chip and dump the contents. Removing the NAND chip would allow the entire filesystem contents (even /) to be manipulated however you see fit. iCloud account information is stored in the following files under /var/mobile/library/accounts :Accounts3.sqlite, Accounts3.sqlite.shm and Accounts3.sqlite.wal; as well as the files found in /var/mobile/library/ConfigurationProfiles: ClientTruth.plist and CloudConfigurationDetails.plist. Deleting these files (either via a native filesystem browser on a jailbroken device or via removing the NAND) followed by a reboot will cause the device to have no knowledge of the previous account, but that does NOT mean the Apple's Servers still don't know about it. The very second it connects to the internet it will remember and lock down again. The same methods used to overwrite previous owner information like we do with MacBooks cannot be performed with an iDevice because of this reason, it has to connect to the internet to be able to log in with a new account but the second it connects online it remembers the previous info so its a catch 22. Plus removing the NAND chip and altering the contents still really isn't a bypass since who wants a shiny new iPod 6s with no possibility for internet access, kinda defeats the purpose of owning an apple device. So I'm sorry iRizwan for making this seem again like I'm just calling you out but I really just don't believe you at all when you say you can do it yet have given zero information to backup your claim except for public information readily available on Google.
SOFTWARE
There are multiple methods to bypass iCloud via software. Granted there is not a single program out there (at least not anymore) that is a simple one click solution and magically your bypassed. For Windows users your best bet is to try a "NAND attack" method by a CFW (Custom FirmWare) restoration, but the success with this is VERY limited. The idea behind this lies inside the actual .ipsw files. Ever heard of "keys" for an iDevice? Well an ipsw is basically just a fancy named .zip archive containing everything needed to upgrade the device and perform any communication between device, iTunes and apples servers. Its literally as easy as just renaming an .ipsw to .zip and you're able to extract the contents, but viewing/modifying them is where you need keys. Keys are literally just that, the keys to removing the encryption on the files found within. Keys aren't available for every device, and about 99% of 64-bit devices have no publicly available keys so that rules out anything past the iPhone 5c. But for the files that keys are available for you would just use either Ge0Sn0w's F.C.E 365's Firmware Manager tool or other standalone programs available over at theiphonewiki.com, decrypt the root filesystem .dmg, either delete or patch /Applications/Setup.app, re-encrypt the .dmg and then restore with either llibimobiledevice's idevicerestore.exe or attempt to restore with an older version of iTunes. There are a multitude of checksums that prevent this from happening. So don't expect it to just be that easy, and 99% of devices just flat out will not work on and there really is no data to say which ones work better than others other than 8gb and 16gb storage devices seem to work better. Mac users are pretty much SOL because libimobiledevice doesn't function the same on OS X like it does on Windows. There is a lot to be learned about the CFW method, and if you have an iBoot or Bootrom exploit that you yourself have created then this method is the one for you, but seeing as how nothing like that has become publicly available since the days of the iPhone 4 its not likely to happen any time soon, I'm thankful that Pangu even came out with a JB for up to iOS 9.3.3 and even that took months and months to release something that Apple patched the very next couple of days!
There is only ONE universal way to bypass iCloud that I have ever encountered in the many years I have been looking into this subject (other than like I said knowing someone that has access to GSX), and I can 100% personally confirm the legitimacy of the method because for months I used to send my devices to somebody I met on eBay. I tried for a very, very long time to get in good enough with him to learn his secrets behind it and even though I got some pretty good clues as to his process I still have yet to figure out how to do it. Here's what I know about this method for those who are interested:
-There are 2 types of iCloud lock, and the only way to tell is to have a locked device be restored through iTunes and become locked at the activation screen: devices that say "Please sign in to the previous iCloud account for this device", and devices that say "This device has been lost and erased. Please contact the original owner". The latter of the two cannot be done. This state is achieved when the original owner signs into iCloud.com and says "Lock and Erase". These devices are probably hot anyways so if you have any that say this I would just recommend tossing them.
- The first iOS to introduce iCloud Lock was issued AFTER iOS 6.1. So if someone were able to figure out how to force downgrade a device to accept an iOS 6.1 ipsw then (and this is fact, not theory) the device would not know anything about iCloud lock and report that information to iCloud where it would then be stored. After this all you would have to do is update the device back to whatever currently signed ipsw thats publicly available from Apple and boom, your through.
I've been trying to develop my own method involving the modification of the activation info via apps like WireShark and Fiddler2, then replaying specific packets back into iTunes that would trick it into activating the device. Gadget-Shows has maybe 1 or 2 videos showing this technique but even with as much that is shown in the videos its not as easy as it sounds. My theory behind a working method would involve a combination of libimobiledevice, fiddler2, and packet modification that would allow a successful downgrade via older iTunes such as 12.0 (because later versions are patched, Apple is on their shit when it comes to this topic).
So I apologize again iRizwan but seeing as how you have provided nothing to back up that you know a little about the topic I am going to have to say that you don't know what you're talking about, in of course the nicest and most respectful way possible. And please, by all means, I absolutely invite anybody to prove me wrong. I'm no genius on the subject and have very much to learn myself, so if anybody else has anything to add i would very much love to hear that I'M the one that is misinformed because i've pretty much lost hope in this matter at this point lol