Nokia 2125i / 2126i / 2128i

I'm sort of new to wireless shopping. What's ESN?

Here's my situation: I already have Verizon service, but my phone is pretty beat up so I'm looking for a cheap replacement.

Since they've taken the 2128i down from the VZW website, I've tried looking into replacing my phone with the prepaid version of the 2128i. Here's what I've been told so far:

1) At one VZW store, I was told that I can have my current phone number transferred to a prepaid phone for $15--simple.

2) At Best Buy, the sales rep told me that it wasn't that simple to convert a prepaid phone into postpaid phone, and that they have to be "unlocked".

3) At another VZW store, I was told that prepaid phones aren't "supposed to" or "can't" be changed from prepaid to postpaid because of some technical detail which I can't remember. He then said that even if I could, with all the charges for the first month service prepaid ($50), the activation charge ($35), etc., it would all end up being close to regular retail price anyway. Can anyone verify if what this guy is saying is true or if he's just blowing smoke up my butt?