Re: does t mobile note 3 use different sim than at&t for straight talk
I'm pretty sure the sim would be different. While T-Mobile and AT&T have some overlapping frequencies so there is some cross compatibility, you would be better served with a SIM that supported the full frequency spectrum of the carrier.
Further, if you bought your Note 3 from T-Mobile and are trying to use it on STraight Talk with an AT&T supported SIM, you'll still have some trouble as the Note 3 had different modems for different carriers.
You'd have had better luck buying an unlocked international Note 3 for this sort of use I think.