Windows Phone 7 handsets were just recently released, and the devices have already been rooted.
According to reports, hounsell from XDA-Developers that a Samsung application ran on a code set that was unlike the other third-party apps, which are based on Silverlight.
Long Zheng of iStartedSomething says:
Upon closer inspection, (hounsell) documented some interesting characteristics of the application that gave it its native capabilities ‚Äì most notably a DLL called ‚ÄúMicrosoft.Phone.InteropServices‚Äù, which if poked the right way provided COM access.
We knew the jailbreak was inevitable, but now that a developer has gained root access, we can be sure that a jailbreak may not be very far off.