Can I use the same cell number as my Android phone with an Apple Watch Series 3?
Actually, what you want to do has already been done. It is possible, but not recommended. Below I will explain how you can get this to work, and then I’ll explain why it’s probably not worth doing.

Before you begin

Before you begin, you will need all of the following:


access to an iPhone 6 (or above) that is running iOS 11 and is unlocked (or, if locked, is on the same network as your Android phone)
an Apple Watch Series 3 with LTE
your Android phone (but it must be an Android phone that uses a microSIM)


Obviously, it goes without saying that you also need to be on a network that supports the Apple Watch Series 3 LTE models (which you already say you are).

What you need to do

Follow these steps to setup your Apple Watch Series 3 with LTE on the same mobile number as your Android phone. Note that these steps assume you have a brand new Apple Watch that has yet to be setup.


Remove the microSIM from your Android phone
Remove the microSIM from the iPhone you’re using
Insert the microSIM from your Android phone into the iPhone
Wait about 30 seconds or so for the iPhone to register your mobile connection
Open the Watch app on the iPhone
Press and hold the side button (not the Crown) of your Apple Watch until you see the Apple logo appear (Note: This may take a while, so be patient)
Once it’s on, ensure you have the Apple Watch and iPhone close together
On your iPhone, tap on Continue when you see a message about setting up an Apple Watch
An animation will appear on your Apple Watch screen. Hold your iPhone over it so that the animation is centred within the viewfinder on your iPhone.


Once it is paired, select whether you eat to wear the Apple Watch on your left or right wrist
When the terms and conditions appear, tap on Agree
Now you’ll be prompted to tap on Agree again
Follow the rest of the prompts to sign in with your Apple ID, create a passcode, set up your Cellular (or Mobile) connection, etc.
Eventually you will see an Apple Watch is Syncing message. Be patient while this process finishes, as it can take quite a while!
Now remove the microSIM from the iPhone and re-insert it into your Android phone
Wait about 30 seconds or so for your Android phone to register its mobile connection



Now you should be able to use your Apple Watch with the same number/network of your Android phone. 

Why it’s not recommended

There are a number of reasons why using an LTE Apple Watch with Android is not recommended. In summary, the three main reasons not to do this are:


Your Apple Watch’s battery life will be really bad as it’ll be relying on it’s cellular connection the whole time, as opposed to using a paired connection with an iPhone most of the time
All your health and fitness data will remain on your Apple Watch and can’t be synced with any of your Android apps
Because of the above two reasons, your overall user experience will be poor!


Further reading


Set up your Apple Watch 
Set up and use cellular on Apple Watch Series 3 (GPS + Cellular) 
How to use an LTE Apple Watch with Android