CELLULAR setup documentation - resolved

I bought Watch series 4 GPS+CELLULAR on the release day 21 September 2018, Friday from the Apple store. I had the following troubles connecting to the cellular. I have AT&T and it took me about 2 hour in the apple store and Apple Tech Support, and 4 hours with the AT&T store and AT&T tech support to resolve this issue. Once it started feeling like longer than usual, I decided to document how I troubleshooted this.

Hope this helps somebody who is having trouble setting up the cellular.

Primary requirements:

Now this is more like pre-requirements,

1. iphone with iOs12 installed. Apple stores does get this done for you at the store, they have the install available in their laptop ready to be copied over to your phone but you have to believe apple store device won't delete your contents and I would suggest you have an icloud backup before you do it. You can also use their wifi but remember they have lot of customers at the store using their wifi and iOS12 do take quite a while. So, its best to do it prior.
2. Postpaid plan. Now this you can talk to your carrier before or after purchasing your device. They should be able to convert your prepaid to postpaid even after you purchased your new watch. But, it is best if you do it prior since some cellular networks have more rigid terms on the postpaid approval process and can take a while. Now, for AT&T it was pretty quick approximately one hour to get switched if you are approved.
3. DATA. Make sure on your postpaid plan you have your cellular data plan activated. Remember you can have a phone without a data plan but for the watch you will need a data plan. You can choose your data plan as per your usage.
4. Device specification. series 3 and series 4 with gps+cellular requires iphone6 or later. Now that we discuss about device, I would like to remind that with iOS12 installed you will be able to use Animoji only from iphoneX or later.
5. 'Watch' app. Remember to install the 'Watch' app from AppStore.

GET THE WATCH:

If you have all the pre-requirements, great job, now go ahead with the apple watch. If you haven't purchased it yet, buy it. And once you open it and follow the general instructions, it should be pretty simple to get the basic setup done. You can easily get the watch to serve as the normal watch. I'm only documenting the cellular connection part here.

During your watch setup if you encounter the following error message, click 'Continue' and finish the other setup. After the watch is setup, follow through the troubleshooting to fix the cellular.

connecting cellular:

1. keep the IMEI, EID, Serial number, and model number handy. These can be found at the back of the box and are very important to make sure your setup is right.
2. On the 'Watch' app, go to 'Cellular'. Make sure you can see your cellular plan on the screen. If you see AT&T with a loading or error message like in the following two screenshots, please contact the AT&T technical support.
3. Once you contact AT&T tech support, they will make sure they get your IMEI and EID numbers and get you phone number linked with the APPLE WATCH. Basically, they will give your watch a number in the backend but will make a 'NUMBER-SYNC' so that you are able to use the your existing phone number on both your watch and mobile. You maybe asked to turn off and turn on your devices during this process. You may even want to try unpairing the apple watch and pair the watch again.
4. Now, go back to the main menu on 'Watch' app and go to 'General>About' and make sure that you can see your IMEI, EID, ICCID, SEID, Carrier details. If you see one or more numbers missing, call AT&T support and verify they have the right IMEI and EID numbers. DOUBLE or TRIPLE CHECK that they have these numbers right. Now, I know these are some large numbers and will be difficult when you are troubleshooting. I highly recommend using a different phone or use a laptop or the AT&T store phone to make these calls to the AT&T technical Support team since you will may at time have to restart your phone during the process. Patience will be your friend.
5. Retry going to 'Cellular' option to see if you find your plan. example, "ATT". If you can click on it and follow through the steps, LOGIN, NUMBER_SYNC, PLAN SELECTION, AGREEMENT, EMERGENCY DETAILS.
6. During this process, you may encounter other issues like APPLE SERVER down. or simply server down. This should go away in a few minutes because this weekend will be a heavy load on all the servers APPLE and network Carrier. But yeah, you will need both the servers at the same time working for you. Attached image is an example.
7. I encountered these issues several time during the setup and in most case you don't have to contact 'Apple tech support' mentioned but you may need to if the issue occurs for more than 24 hours. But keep retrying the cellular setup as mentioned in step 5. Once you go through all the steps, you should see the plan details and your usage info. You should also be able to see the info from step 4 on the 'Watch>General>About'. Try placing a phone call after turning-off iMessage and turning-on airplane mode on the phone settings. If your watch can make calls now, Voila! YOUR WATCH IS ALL READY NOW.