After making a big deal of this new feature at CES, SCEI has announced that they are delaying the introduction of Skype
to the PSP. Originally planned for release tomorrow, the feature has been delayed ... in Japan, at the very least. The two Skype headsets being manufactured for release in Japan "did not meet the Skype specifications" and therefore, cannot be released.
With a delay in Japan, one can assume that the new firmware update will be delayed worldwide. Those anticipating free PSP-to-PSP calls will have to wait just a little longer, it seems. However, maybe we'll be surprised by a firmware release that comes out in the rest of the world. Considering that has never happened, we won't hold our breath.
[Update via Kotaku
: This announcement "will make no difference to the European and USA launch, which will coincide with the end of January firmware upgrade." Thanks, Espiox!]