Can any iphone model use my old sim card and old phone number?

I'm thinking of getting an iphone for college cus some of my classes uses tophat which has an app for students to respond to questions when asked during lectures.since the lecture hall has over 300 students each, there's no way the professors can know who is who in a large audience. So my question is can I use my current phone number and sim card for any model of iphone without changing my existing phone number? I'm only thinking of getting an iphone and an iphone only, no androids or other types of smartphones

Well it depends on the SIM card you are talking about as well as which iPhone you intend to get.

iPhone, iPhone 3G, iPhone 3GS - miniSIM (standard sized SIM)
iPhone 4, iPhone 4S - microSIM
iPhone 5 - nanoSIM

^^^ the iPhones & the SIM cards they use. If the iPhone you are getting does not match up with the SIM you have you could have the carrier issue you a new SIM of the correct size with the number assigned to it.