Yes, you will need SIM card when you Bring Your Own Phone from a non-Sprint/Boost Mobile wireless provider.
An unlocked smartphone isn’t tied to any specific carrier or contract.
The BLU S1 is an Unlocked Smartphone. Compatible with AT&T, T-Mobile, Sprint, Boost Mobile, and entire MVNO network.
You can find the IMEI and MEID by dialing *#06#
Please visit your nearest Sprint store to get your phone activated. In order to find your closest store, please visit this link; http://storelocator.sprint.com/locator