I know this is a very old thread, but this issue came up for me recently.
The agent I spoke with a USC said that unlocked Samsung phones are specifically blacklisted when it comes to using them at US Cellular. The only phones that are available for transfer are ANY iPhone, the Google Nexus series, Motorola, and the mainstream HTC phones. (Not the cheap free/one dollar phones).
No Samsung device at all is accepted from other carriers, unlocked or otherwise. For me, I found that Verizon and T mobile accepted the following unlocked phones from me, which were previously from AT&T:
Galaxy S4 Mini, Galaxy S4, Galaxy S3, Galaxy S5, Galaxy S5 Active, Galaxy Note 3, Galaxy Note 5, and Google Pixel XL.