How to switch from verizon to att and keep the same number?

I have an iphone 4 with verizon and i'm on my moms and step dads plan and i want to switch to att and have my own plan soon and keep the same number. I don't know if i want an iphone with att or the galaxy note 3

Enter your info on the AT&T website to learn more: http://www.att.com/...umber.html