Sorry to hear that. Good luck out there!
However, it is most likely due to Network Vision upgrades in Chicago, which are moving at a very high pace in the Chicago market. According to S4GRU, there are a small handful of markets that are going to experience dropped calls as a result of the upgrades. (If my memory serves correct, its about 5 markets out of the whole country, and I believe it is those that have Motorola legacy equipment.)
Here is S4GRU's article on that: Sprint battling Network Vision deployment woes in the Windy City - Sprint 4G Rollout Updates