According to Capture Integration...
"Phase One & Leica Form Strategic Alliance
The just-announced medium-format Leica S2 will feature sensor, software, and firmware developed by the experienced engineers of Phase One and will be distributed exclusively through Phase One channels."
http://www.captureintegration.com/According to David Farkas (who attended the Leica VIP launch event of the S2)...
"So what’s the deal with Phase One? The truth is that I’m not sure, right now (and neither is Leica or Phase). The S2 was developed 100% in-house. Leica is very proud of this. The hardware engineering to the optics to the firmware was all done in Germany. With the Phase deal, the S2 will shoot tethered into C1, which is nice, but they certainly didn’t create this product – Leica did. There was mention of Phase dealers carrying the camera, in addition to Leica dealers, but this is not certain right now. Time will tell.."
http://dfarkas.blogspot.com/And the real story? As Mr. Farkas says, time will tell. As a side note, just because two companies have a "strategic alliance" does not mean that one company is developing the other's products. Phase One has a strategic alliance with Microsoft, but I don't believe that Microsoft's experienced engineers are producing major portions of Capture One software or that Phase One is a lead developer of Vista.
You can sort out the "truth" among the active posters here. I'm overloaded with other obligations.