Sony has announced plans to open up the UMD format, albeit limitedly, to 3rd parties. For the time being, Sony is not only pushing companies to release movies & music in UMD format, but also to develop UMD-based media players, providing a larger incentive to by into the PSP. However, Sony is still unwilling to support 3rd parties interested in developing additional software (e.g. browers, chatting platforms, etc.).
