I'm sorry to hear about the mishap with your phone. That's disappointing.
You are able to activate another device to run out the remainder of your contract for sure, providing the SIM card is compatible between the iPhone 5c and the S4. Do you happen to have our insurance feature on your account? If so, if it's just recently happened (in the last 60 days) you're able to make a claim pay the deductible and receive a like for like device instead.
If you'd like me to take a look and confirm, be sure to send me an email to firstname.lastname@example.org with the details of your account and I'll look into it from there.
The iPhone 5C apparently uses a nano SIM (smallest size) while the Galaxy S4 uses a micro SIM (second smallest size).
Also the S4 will need to have been used on MTS before or be an unlocked phone. If it was previously used with a different company it may need to be unlocked.
Cory is right, the S4 would need to be an old MTS phone or an unlocked device if it was previously used with another provider.