Will an Unlocked Galaxy S21 Ultra 5G work on Xfinity

Thanks for the tip, using the xfinity mobile app. Pairing SIM to new device in progress, indicated can take up to 6 hours. Hope this was the solution.

I have got three S21 phones directly from Samsung with S9 trade ins. I called and spent an hour with teir 1. Was told about not being compatible because phone was not purchased from Xfinity Mobile. There was argument on how S21 purchased from Xfinity is different since they get it from Samsung. I was transfereed to Teir 2. There was back and forth and eventually Teir 2 person got green light from her supervisors that S21 is indeed compatible. Then it took 2 hours to get it to work and show up on my Xifnity Devices page. Teir 2 person said they have not done this type of activation before and for every error she had to put me on hold and get guidence from somewhere. 

Yesterday I got second phone, called teir 1 again and asked to get transferred to teir 2. The teir 2 person said this is her first week on the job after training. She asked her teir 2 supervisors for help and was told the S21 phone is still on pre-order and there is no way it can get activated even if it was compatible. I asked how do you explain S21 that was activated yesterday and showing up on my Devices pages. Answer was we don't know and not all devices are created equal. I did not wanted to argue or waste my time. So i disconnected and now i have 2 phone that are not activated and one that is activated and working. I am not sure what i am going to go from here. 

I called and talked to tier 2 on the 27th when I got my phone.  They tried to force the IMEI in, but I noticed today that it had gone away under my account, but I tried the pair option, and my cell service immediately dropped. It came back up a short time later after I restarted my phone, but tier 2 says it may take some time before billing recognises the SIM.  It's weird that the pairing system recognizes the SIM and detects my model, but not the billing side.

I feel like I am in the same boat. I hope Samsung and Xfinity can work together to get this fixed. 

Noticed today, I have no mobile data, only wifi and phone still shows as incompatiable. I can make calls, receive and send texts. At this point I don't know what else to do here.

Update: Finally spoke w/ a manager at XM, they are in the process of adding all the unlokcked phones/red-tape from Samsung w/ an ETA of 02/09/21. She indicated that is why my mobile data is not working and created an appointmnet to follow-up w/ me next week.

I think I am going to do the same, switch to Verizon, just tired of the BS from XM. Checked my status/compatiability on Verizons web site and I am good to go, plus the $300 e-gift card is nice...

Thought I'd give them one more chance and called customer service again, figuring that after 4 days they might have a reasonable and consistent message for all of us affected by this debacle.  Well they fell flat again telling me it was not compatible.  Now, just so it doesn't get lost here is the original message direct from Comcast/Xfininty wesite stating that you COULD order directly from Samsung

Well you must have gotten really lucky, because all I keep hitting is a brick wall with these people.  even using this forum and your story as further evidence, but they just don't get it.  

Now the old deactivated lines and devices are gone, just showing my correctly-provisioned S21 Ultra.