US Cellular is a
CDMA provider, is that correct? This means the phone does not have a
SIM card to swap into another "unlocked" phone.
CDMA phones are instead activated through your carrier by the
ESN (electronic serial number), and they usually maintain a list of ESNs that are okay to be activated on their network, which does not include other carriers' ESNs.
What that means is, they probably will not activate a non US Cellular phone, but you'd have to call them and ask to find out for sure. Most
CDMA carriers, at least in the USA, say other carriers' phones will have problems on their network because it thinks it's roaming all the time. Sorry I don't know much about US Cellular, they're nowhere around where I live, in fact I had to guess half a dozen zip codes to look at their plans before I found a major US city they provide service in.
That's just how US
CDMA carriers are in general, hope this helps you figure it out.