Are iPhone 5cs locked to a phone company without a sim card?

Or does it depend what sim card you're using?

Same deal as with almost any other mobile phone: if the purchase price was subsidised by a carrier then they'll usually lock the handset to their network to force you to buy your services from them in order that they can recoup their investment.

The iPhone 5c could be supplied by Apple as a factory unlocked phone sold to customers at full price, or they could supply them to mobile phone companies locked to their networks so that the phone company could the sell the phone with an airtime contract package.

So the answer to your question is this: The SIM card is irrelevant as the iPhone 5c was sold in both subsidy-locked and factory unlocked variants.

IPhones are sold unlocked in particular cases, so the SIM doesn't matter in those cases. Most times though it is sold locked, depends on where & how it was configured.

Lol, you think its just the sim card?

If your buying new from the phone company then it'll come with a SIM card that you install and activate.

If you buy the phone used and locked then you will have to buy the sim separately from the service provider. This is because no one is going to sell u their phone and include their SIM card with all their info on it.