If you're with Sprint, you don't have many options for unlocking your phone's SIM card slot; if you can do it at all, you're limited to service on foreign networks. You'll have far more flexibility in the near future, though. The carrier has revealed that it will unlock devices for American use starting with those launched on or after February 11th, 2015. The move will let you use SIM-based features (such as LTE data) on AT&T, T-Mobile and other US providers as long as your device supports the right frequencies. Sprint's prepaid brands, including Boost Mobile and Virgin Mobile, will also offer the added freedom.