Is it possible to set up Apple Watch Series 3 with a separate phone number?

Hi

No, it is not possible to set up Apple Watch with a different phone number.

Apple Watch Series 3 (GPS + Cellular) has an embedded SIM / eSIM that copies information from the paired iPhone's SIM card.

The cellular features require a cellular service plan for the paired iPhone that also specifically supports Apple Watch (including the carrier activating the watch on the plan):

Apple Watch - Carriers - Apple

I was looking to do the same thing. I spoke with a rep at AT&T and they told me that I can add the apple watch to the plan, then after it is active on the plan, cancel the wireless service on the phone and just keep the service on the watch. It will actually save $15/mo, as the iphone cost is $25/mo on the plan and the watch is only $10/mo. I will see if this actually works on the 22nd. I am purchasing the watch at AT&T to make sure it works, if it doesn't work, I will just return the watch right then.

I'm not sure if other carriers have different plans, but T-Mobile said they will set up the Apple Series 3 with either its own number or so that the watch can share both your iPhone's number and its own number. I'll give you a definitive answer tomorrow. My watch is due on the 22nd and T-Mobile said they will turn it on then. I'll update when or if they fulfill their claim.

Yes you can do either or. Digits plan to share the same # and TMobile One Wearable Tech Plan for a separate #. But the later is $20 per month while Digits is free 3 months and then $10 per month. I am speaking from having tried them both. I stayed with Digits as I don't want people to get calls and texts from a # they don't recognize when the watch is in cellular mode. When the watch is connected to your phone under either plan it will use the phones for calls and texts.

Yes it is with Verizon. You have to add your watch to your carrier account with a seperate # from your iPhone. You will need your IMEI number and E-SIM # (on sticker outside of box). Presently, this is the work around until Apple fixes the activation glitch. I was fortunate in having an unused # on my account, which I was already paying for. It took over 2 hours for the Verizon's associate to complete ( 4 unpairing /pairings) with numerous calls to support.

The only issue I have experienced has already been previously mentioned concerning no connections with unauthenticated WIFI's. It happened to me with Comcast/Xfinity hotspots. Once I disabled this wifi on my phone, the watch no longer had connection issues. Messaging, Phone and Maps worked every time.

Sam_nj: Can you tell me who you talked to at T-Mobile? I called Tech support and they sent me over to their Digits group. The Digits group said you can have a separate number, but it is only a data "placeholder," when you dial out, it will still use your phone's number and you can't be called on the iWatch's number. They said that they had a plan that worked on the Samsung phone - talk and data plan - but it didn't work on the iPhone. I don't know if no one knew how to set up an iPhone or maybe I should never call on a Saturday.