If i buy an iPhone separately from verizon can i still keep my unlimited data?

I currently have an iPhone 4 with unlimited data with verizon and i want to know if i buy the iPhone 4S say from the apple store and get my number switched to that phone will it completely switch my phone plan or can i keep my unlimited data for the same price?

I heard you need to pay full retail for the device you want the grandfather plan on

  • Will my cell phone plan with verizon be cheaper if I get the iPhone separately? I plan on switching to Verizon soon, yet I will be on a budget since I'll also be living on my own for college. So my question is, can I open up an account with Verizon, buy a cheap phone with data and texting etc. On it, THEN buy a Verizon iPhone off of ebay? Also, how much would the monthly charge be if I was to buy an iPhone 5 with its plan at Verizon?
  • What can I do to keep my unlimited data plan on Verizon and upgrade to the iPhone 5? Now I already know that I can buy one full price from Verizon for about $649 but I don't want to go that route, and I don't want to buy a subsidized iPhone 5 and end up losing my unlimited data plan. Would I be able to just wait and buy a used iPhone 5 after it comes out and then have them activate the phone on my account? They wouldn't be able to take away my unlimited data would they?
  • If I buy an iphone separately can i activate it on verizon? So I have an iphone and data plan already. If i buy myself another 4 (because mine is broken but usable) will i get charged if i activate it? Like basically if i replace my already activated iphone 4 with a new iphone 4, will it cost money?
  • Can you buy an ipohone separately and have tmobile connect it for you? Basically I want to buy a refurbished iPhone 4 or 5 and cuz I hate the aspect of having an iPod touch and a Samsung gravity cell, and want to be able to play music and do my txt and web all in one. Can I buy my IPhone somewhere else and bring it to tmobile to transfer my account over?