Join the new Xfinity Rewards program and get a reward based on how long you were with Comcast and other factors. Spefically, Xfinity Mobile customers are reporting seeing a reward of $50 or $100 Visa gift card. Some Mobile customers are also getting a device credit.
Xfinity customers from other services, e.g. internet, are just getting smaller rewards such as coupons, sweepstakes, and movie rental deals.
You can probably continue getting small rewards if you keep checking your Xfinity Rewards periodically, but this one-time $50 or $100 Visa gift card for Mobile customers is especially worth looking for.