You can call your carrier and request they unlock the device('s bootloader). There are also a few services that you can send some information to that will unlock it for a small fee.

These sorts of shenanigans are a big part of why I haven't had any desire to switch from my S3, since even with the neat specs, you could hardly call swapping performance, personal control, and extensive added functionality for bloatware and unalterable permanently out of date OS versions an "upgrade".