Yahoo is set to revamp its two primary mobile services and will today launch documentation that will let any developer or publisher write mobile widgets for the Yahoo services.

Yahoo users can access its services from their phones in two ways: through a browser or through Yahoo Go, an application that users download to their phones. Both products are getting facelifts.

It hasn't changed much over the past few years, but the new Yahoo mobile home page will be customisable, said Adam Taggart, a director of product marketing at Yahoo.

Users will be able to choose 'content modules' that will appear on their home page, displaying content such as the latest bid on an eBay item the user is tracking. Clicking on the module opens a widget that feeds that information to the page. Users will also be able to place frequently used links on their home pages.

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Yahoo Go, the downloadable application, is also getting an overhauled look and feel, Taggart said. In addition, from today the Yahoo Go client will begin showing display advertisements to users.

In addition to the new look of the mobile web page and client, Yahoo plans to release documentation that will let third-party developers build mobile widgets. Over the next couple of weeks, Yahoo expects to release a more robust software development kit, tools and support, Taggart said.

Developers will build the widgets using Yahoo's own XHTML-based programming language, he said.

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End-users will be able to choose widgets from a portal much like Yahoo's existing PC-based widgets web page. They'll be free to use, but developers will be able to include display ads and sponsored search in their widgets to earn revenue. Yahoo even plans to support other competitive advertising networks if the developer or publisher has an existing relationship they'd like to maintain, he said. "We'll build a plug-in so you can bring that in," Taggart said.

The new widget development offering is Yahoo's attempt to solve the fragmentation issues that plague the mobile industry. Building mobile applications is hard, but only the first hurdle, Taggart said. "Once the experience is built, you have the much larger and painful problem of scaling them across the different device types out there," he noted.

Application developers must rewrite or tweak their applications for the various operating systems and even for different handsets running the same OS.

The Yahoo Go client runs on more than 250 phones, and the browser-based service runs on many more phones because it can be accessed from a browser. Users of either Yahoo service will be able to access the new widgets, offering a large market to developers, he said.

Widgets, however, typically don't offer the same types of capabilities as full-fledged applications. In the future, Yahoo hopes to allow developers who create widgets for the Yahoo Go client to access native phone resources such as the address book and location information from a phone's Global Positioning System (GPS) radio, Taggart said.