What is Reddit's opinion of BlastCase Nano to Micro/Normal SIM Card Adapter for Apple iPhone 5 4S 4G 3GS 3G?

From 3.5 billion Reddit comments

Short answer: AT&T uses SIM cards. Take SIM card out of old phone, put it in new phone. Voila. (assuming the two devices use the same size SIM card......)

Long answer:

The beauty of SIM cards is allowing you to switch between devices easily, unlike CDMA carriers like Sprint and Verizon (although they may have made the transition over to SIM card use with LTE).

One thing you need to be concerned about with switching to a new phone is making sure it supports the frequencies/bands of your carrier. I'd imagine you'll be buying an AT&T GoPhone version of the 640, so you don't have to worry about incompatibility with AT&T. It'll work right out of the box. Also, unlocking is only for using a phone on a different carrier than the one it is locked to. Being an AT&T phone, you don't need to unlock it from AT&T to use it on AT&T's network.

Another thing to consider is the size of the SIM card. You'll need a microSIM for the 640, and I believe your Galaxy Alpha uses a nano-SIM. You'll need an adapter.

I have this item from this seller:

http://amazon.com/gp/product/B009B9YWB4/ref=ox_sc_mini_detail?ie=UTF8&psc=1&smid=A2YLRJ3IT9MQBP

It arrived quickly and does what it's supposed to. Don't really have more to say than that.

http://www.amazon.com/Micro-Normal-Adapter-Apple-iPhone/dp/B009B9YWB4

Ignore that it says Apple. It's the same damn thing

This should be all you need.