Can I swap out a iPhone 4 sim card into a iPhone 5 with the same carrier?

Question

Here is the situation.  I used to have Sprint as my personal cellphone carrier and just had bought an iPhone 5 when my employer put me on a business cellphone plan that they pay for.  They bought one of the bargain basement original iPhone 4 handsets (not to be confused with the 4S) for employees to use, also on the Sprint network.  The phone is owned by them; the plan is paid for by them.  We just get to use it.  As a result, I decided to just close out my personal cellphone account, even though it was a better phone.  I used my 64GB iPhone 5 as my iPod, it worked great for music, apps, books, etc that I needed, and I just used the 8GB iPhone 4 just for phone calls and text messages. 
Well recently, with the 5C and 5S being released, I wanted to know if the iPhone 4 could be upgraded by my employer to a new handset, preferably a 32 GB 5C or a 16 GB 5S.  My employer has been slow to respond, because there are so many employee accounts to weed through and most are perfectly fine with an older phone.  I am not, because the new operating system is slower on an iPhone 4 than an iPhone 5.
I want to ask my employer if its possible to get the SIM card from the iPhone 4 just swapped out into the iPhone 5.  Is that possible?  I understand that there is a size difference in the SIM cards.  Is this something I could do myself, just pop it out and pop it in in the new handset?  Or is this something that will require going to my employer to do, or to a Sprint store and have them do it?  Do I have to be concerned with warranties being voided if I want to do this? (Keep in mind the iPhone 4 is my EMPLOYER's property, and they pay the bill as well.  My inactive iPhone 5 is MY PROPERTY and has no current cellular service.) 

Answer 1

I want to ask my employer if its possible to get the SIM card from the iPhone 4 just swapped out into the iPhone 5.  Is that possible?
No, iPhone 4/4S uses micro-sim and iPhone 5/5C/5S uses nano-sim.