Not to be left behind in the era of the iPhone and Google Android, Yahoo! recently launched the Yahoo! Mobile Developer Program, which lets developers create widgets that users can install within Yahoo! Go 3.0.

Instead of negotiating all the multiple device models (and carrier restrictions), this enables developers to create widgets using a simple XML based API and enable end users to install those widgets within the framework provided by Yahoo! Go.

For more details, check out the developers page and the blog.  

As the inagural post on that blog announced:

This is a huge deal. Anyone will be able to write a Snippet or Widget and deploy it across hundreds of phones, potentially reaching millions of customers you never could before. We take care of the hard part and let you focus on what you do best: content.