Upgrade iphone by switching sims?

I have a company iPhone 4s from sprint. I also have a personal cell phone but am tired of having to pay for it and carry two phones. I want to upgrade my work phone but my company doesn't want to upgrade me. If I buy a 5s or a 6 myself is it possible to just swap SIM cards into it? Would my company notice anything on the bill if I did this without them knowing?

Won't work. Your work phone is locked (programmed only) to work on just Sprint. Same with your own phone. You would have to buy a Sprint iPhone and have the work number ported to it. They wouldn't notice on the bill but there's no way to have 2 numbers running to one phone. Best luck.

Locked man