There are a couple of online retailers in the US offering preorders on unlocked 950s, B&H being one of them. They're estimating a shipping date of mid-December.
Microsoft isn't providing any info on pricing or availability because they have an exclusivity deal with AT&T. It's possible unlocked phones will be available from them in mid-December, like those other retailers, but I don't think that's been announced anywhere.
It's a bit of an odd launch, if you ask me.