That is exactly what it is - an ATT compatible ST BYOD sim purchased from ST.
Someone on here said they liked to swap phones often, like almost daily, amongst a handful of cell phones they own. SIM went into different phones. They received a call from Straight Talk asking WHY they were switching so much, just making sure there was no fraud attempt going on or something.
But yeah, you can do it without changing anything.
The call from ST was because the person was rotating the SIM among several phones. Even then, the person was able to do it with no problem. Straight Talk just wanted to know why, as they considered that strange behavior.
Sent from my Samsung Galaxy Nexus (GT-i9250).