Didn't Andy Rubin make a comment at the Google IO event in May, that this Fall all four U.S. carriers would see their own release of Android 4.0 "Ice Cream" phones ? We do know that Verizon is getting the "Prime" and will be first out the gate with "Ice Cream".
I would bet that Sprint, ATT, and T-Mobile will also be getting some type of Ice Cream phone this Nov/Dec but it might not be the Prime, could be a Motorola or HTC device ?
Big Red is supposedly getting the Droid Prime, the Nexus Prime will (theoretically) be coming to the other 3 carriers.
Its all still unclear as samsung is supposedly making both the Droid Prime AND the Nexus Prime (why would they make two models like that?) but it wouldn't be the first time a model was "renamed" to suit a purpose (Epic 4G Touch). The Droid Prime just got its cert for its WiFi and the Nexus Prime just got its Bluetooth Cert. Its also possible the Droid Prime is just a souped up Galaxy SII for Big Red as opposed to a renamed Nexus Prime. Simply put, there's just not enough data to know for sure yet.
That said, with what the rumormill is holding onto for specs on the Nexus Prime, it sounds like a hands down badass phone that I'm guessing (guessing) would be released a little before the holidays to curb the iPhone5 launch time. The certs are coming in and it hasn't hit FCC approval yet, but phones have been released VERY shortly after FCC approval, so who knows really.
Most of what I got came from gottabemobile.com from an independent technology blogger, but I did enough google-fu to find everything that led him to the conclusion and I would generally agree with his article.