Xfinity Mobile is offering $400 on all Samsung S21 series (and S20 as well) for
New Customer / New Line : Number port in and 24 month DPP required, $400 credit given as monthly credits over 24 months
Existing Customer : Requires buying the phone outright and $400 gift card issued after 90 days of upgrade.
S21 : $399.99 https://www.xfinity.com/mobile/sh...5g-samsung
S21+ : $599.99 https://www.xfinity.com/mobile/sh...5g-samsung OOS
S21 Ultra : $799.99 https://www.xfinity.com/mobile/sh...5g-samsung
You can also get a new line using BYOD and then upgrade to get the existing customer offer (if you prefer that) and dont have a line with Xfinity.
Getting Xfinity Mobile service do require an Xfinity Internet / TV service.
You can still get the upto $200 credits on Samsung.com if pre-ordering from Xfinity:
By 1/28/21, pre-order and purchase a Samsung Galaxy S21 5G, S21+ 5G, or S21 Ultra 5G on device installment plan, 2-year contract plan, lease or outright purchase at full retail price, & receive a Samsung Galaxy SmartTag ($30 value) + Samsung Credit either (i) $100 (S21 5G), (ii) $150 (S21+ 5G), or (iii) $200 (S21 Ultra 5G) ("Gift"). Only available while supplies last. By 2/28/21, using your Qualifying Purchase device, follow instructions on the Shop Samsung app ("App") to submit required info. Gifts will be emailed apprx 4-6 weeks after verification of Qualifying Purchase