Following last week’s PlayStation 3 firmware 1.80 update, a new functionality was introduced which would allow PSP owners to access all videos, music, and pictures on their home PS3 over the Internet, a feature previously available only on a local network. But it wasn’t until today’s PSP firmware 3.50 update that the Remote Play over the internet feature is actually available for PSP and PS3 owners.

After applying the update, you'll need to hook the two consoles together via USB for a certification process, which means that when you are out and about, your PS3 will know it's you calling in from the cloud.
Besides the Remote Feature enhancement the update also includes a new 'RSS Channel Guide' feature under the 'RSS Channel' menu. The new firmware should be available via your PSP's Network Update option.