Yes, it is a manufacturing partner, since they've already announced network partners. I do wonder which manufacturer it could be...

This might be far-fetched, but I wonder whether it is Lenovo. Just saying because Lenovo's PCs and Servers have excellent Ubuntu support.

My wild card guesses would be Lenovo and Dell (which, out of nowhere, made a pretty solid piece of hardware with the WP7 Venue Pro)

The Venue Pro and the contemporaneous Streak Android models were designed and manufactured for Dell by Qisda.

They were indeed very solid pieces of kit, being aimed at the corporate Latitude-laptop-buying market. My Streak 5 is still going strong after four years.