Right now, Amazon has a great deal going on for those looking to add a line or switch to AT&T or Verizon. They are offering a $100 new Activation credit. Now this only applies to new activations unfortunately, and Amazon does state that it may take up to 3 billing cycles for the credit to show up on your bill. But since wireless service is so expensive, and so are smartphones, it's great to have a $100 bill credit, but it still won't pay for your entire bill for a month.
This applies to ALL Verizon and AT&T smartphones at Amazon. So that includes the Galaxy Note 3, Galaxy S4, LG G2, LG G Flex, Moto X, HTC One, and everything in between. Both of these carriers have some great phones, and if you're heading to Verizon, I'd recommend the Motorola DROID Maxx. Yeah, I know I'm a Motorola fan. But if you pick up the DROID Maxx, you would be one as well. That battery life is pretty crazy. If you're on AT&T or Verizon, you can't go wrong with the LG G2, Galaxy Note 3 or even the Moto X. All of which are great devices.
So buy a new phone for AT&T or Verizon through Amazon, and get a $100 bill credit. Definitely not a bad deal. Especially since their phones are usually quite a bit cheaper than buying from the carrier.