Yes T-Mobile is still offering the 3 free months and waived activation. T-Mobile also has another offer where you save $50 when you finance. You are limited to 1 offer of your choice. Both are listed as available for a "limited" time. So they can pull the offer at any time.
Notes on Financing deal: *Qual'g service, credit check, finance agreement, Data with Paired DIGITS™, and iPhone req’d. If you cancel wireless service, remaining balance becomes due. 0% APR. Plus full tax at sale. Participating locations only. Limited time; subject to change. Credits: must be in good standing; allow 2 bill cycles.
AT&T and Verizon also still have the credit back for $30 Activation and 3 x$10 of service for a max of $50 credits applied to your account within 3 billing cycles.
You can also get the same 3 month trial / credit when you purchase your watch from Apple and activate on one of the supported carriers.
Dave