If I buy an iphone used from another carrier ad buy a sim card from my carrier will that work?

I have an iphone 4s with virgin mobile and I want an iphone 5 but all virgin mobile phones are so expensive! I looked on ebay for virgin mobile nano sim cards and they are only around 2 dollars. If I bought one of these sim cards and a used iphone 5 from another carrier would it work with my carrier?

No it won't work because the phone is programmed for that carrier you got it from.

It will only work if the phone you buy is unlocked to all networks or is locked to the Virgin network.

Nope, don't do that. You just use your SIM from iPhone 4S to activate the iPhone 5 or if you're on Virgin US, SIM will not work as Virgin is CDMA. You need to buy a CDMA version of iPhone 5 and have it flashed to Virgin. If you need more info on the phone and activation, mail me for more info.