I believe that the 128GB model will be hard to get.

Fwiw, the AT&T Wireless Live Chat person (Ashley L) just told me the phone (S6 128GB Black Sapphire) should be available to pre-order by Wednesday of next week (April 8). We'll see.

Today is the 8th and you still cannot pre-order the 128GB S6. I called CS, and spent over an hour at the AT&T store dealing with a return of my S6 Edge 128GB. They noted my account and said when its available to pre-order they will take it back without issue. I just can't use it, at all. S6 Edge is on call forward right now, grrrrrrr.