Summary: I love the phone and have no regrets. It is unlocked but has AT&T branding on mine. Calls and data work well on Straight Talk. Texting works through google voice and I don't use MMS, so I know there is a way to set that up but I haven't needed it.
Pros: Love the keyboard, love using Straight Talk on an unlocked Blackberry, quality of the hardware is very nice and substantial (not cheap or plasticy). Q10 software is great, apps load quickly. Phone is responsive.
Cons: The touch screen is very responsive and coming from a non- touch Blackberry, it is taking a period of adjustment. I really wish I had the "band" back - the track pad, call and end keys. I particularly miss the end call key.
Summary: It's AT&T branded, but it is unlocked. I'm using it with a T-Mobile sim card. I get 4G LTE in my area. It's so nice having an actual, physical keyboard again, which is very responsive. It's an SQN100-1 model.