The Skype service which will be released with the nest firmware update later this month will enable the user to make VoIP calls.

“Call friends, talk trash to fellow gamers or catch up with acquaintances via Skype for PSP system.” http://www.sony.com/ces/index.html

Unfortunately this will only be available for the PSP slim and light, so that means people who own the first generation of PSP’s wont be able to use this feature, not for a while anyway.