One of the many differences between Windows Phone 7 and Microsoft's previous attempts at producing a mobile phone operating system is that the new platform's user interface will be locked down and consistent. Windows Mobile handset manufacturers would often use custom front-ends as a unique selling point, but on Windows Phone 7, that won't be an option. The Metro interface that has been widely demonstrated will be the only UI available. A choice of color scheme is likely to be the only real modification possible.
For the handset vendors, losing the ability to skin the interface, and hence differentiate their products from the competition, may well be an unattractive prospect. In response, it looks like Microsoft is going to help them write appealing custom applications to reinstate that differentiation. A job advertised by the company is looking for a developer to work with a Korean OEM (most likely LG, perhaps Samsung) to help produce unique software to win over consumers.
Whatever these custom applications turn out to be, they're still going to be limited in scope. OEMs will be limited to providing up to six applications taking no more than 60MB, and for the most part will be limited to the same Silverlight API as third-party developers. OEMs will have a handful of—unspecified—extra APIs to work with, but even with these, the days of radically different front-ends on Microsoft-powered phones are coming to an end.
OEMs aren't the only developers that Redmond is trying to entice to its new platform. An iPhone application developer approached PoetGamerck.biz claiming that he'd been offered up-front cash to port his successful iPhone games to Microsoft's new platform.
The amount of money was claimed to be substantial, but not enough to justify the porting effort. iPhone software is written in Objective-C and/or C++, using OpenGL ES for graphics. Migrating to C# and XNA (the managed DirectX-like API used for Windows Phone 7 games) is likely to be a sizable undertaking. Perhaps surprisingly, the source also suggested that Microsoft wouldn't have to change too much to make such ports economically viable. Even if true, the fundamentals of the platform—the use of managed code and C#—are unlikely to change in the near future.
Source: ars technica