Microsoft has long counted Sendo as one of its major partners in the development of the Windows Powered Smartphone platform. Microsoft even took a stake in the privately held company last year.
Sendo was one of the first phone manufacturers to announce that they would build a phone running the Windows Powered Smartphone - and the Z100 was somewhat of a flagship device in this space. Anticipation surrounding the Z100 was very high, and the device had been expected to ship within a few weeks.
Sendo has stated that a major reason for the switch is that Microsoft's Windows Powered Smartphone did not offer the level of customization that was required by the carriers. On the other hand, Sendo was able to get the source code for the Nokia software, and they feel that this gives them a higher level of customization than could be reached with the Microsoft platform.