Sony released the firmware 3.50 for the Sony PSP today in Japan.

The Sony PSP firmware 3.50 brings your remote play of your Sony PS3 stored media over the internet. Yet another reason to never switch off your Sony PS3. Do not forget to install Fold@Home if you do so. There is no an additional menu for remote play under the communication settings. The 3rd minor addition is an RSS channel guide.
Via the Sony Playstation Japan site. The firmware might be available later today also on the U.S. Playstation site.

For remote play to work, your Sony PS3 needs to have the latest Firmware 1.80 installed.