Sim card contains personal information like your phone number and contacts. This is good for someone whose sim card has been destroyed or lost. When you put in new sim card to your phone, you have to contact T-Mobile to setup with new sim card. Or let's say you bought a used T-Mobile phone and it did not have sim card, this new sim card will do. Sim card have nothing to do with activation. Hope this helps.
To all interested in this: I am not an expert on T-Mobile service, and I may not be able to answer some questions. T-Mobile number 1-800-866-2453 or www.tmobile.com to get the answers you would like to know.