After doing some research it appears that the discounted Gear S3 offered by other vendors in the non-LTE version.
Thanks for coming back to let us know what you were able to dig up, mjbenz. To be honest with you, the Gear S3 is so new that I haven't seen any user reports regarding the experience of bringing one to T-Mobile, so I'm not 100% on the answer - but in the Amazon reviews for one I scoped out, a user suggests referencing Samsung's site to match model numbers against versions for sale to determine which are LTE and which are not. I'm hoping that other users might have more feedback to contribute, or that your research could save someone else some time! Thanks!