Furikup is a PSP SIP Phone application by Fanjita.

Release notes:

Sometimes it’s important to assert the dominance of homebrew features over Sony’s lacklustre official firmwares.

Take the forthcoming PSP phone functionality. According to various rumours, Sony will shortly announce (in a few regions of the world) some new software to allow you to make and receive phone calls with your PSP via wifi, which may or may not be based upon the popular Skype platform.

That’s nice, but there are a few flaws:

It’s not yet clear how much it will cost to obtain the software, to subscribe to the service, and to make calls
It’s not likely to be available in all countries
It’s rumoured to only run on the PSP Slim – what about all those loyal early-adopters? 🙁
It will probably only support a limited subset of possible voice platforms – e.g. maybe just Skype, which is notoriously bad at interoperating with other networks.

Here at Noobz, we’re fans of freedom. So we thought we’d release our own PSP Phone software – and here it is, codenamed “Furikup” (it’s a geeky protocol-based joke, don’t worry about it).

Here are some of Furikup’s best features:

It’s free software – in both the beer, and speech senses.

You can use it anywhere in the world, subject to signing-up to a suitable local SIP-based voice-over-IP provider and being near a usable wifi access point. In many countries, you can find those for free or nearly-free – e.g. with SIPGate, in the UK, you can call to your PSP from any standard phone (landline or cellphone) for just the standard local call cost, and from PSP to another SIP phone (another PSP or a PC) for free.
It runs on both slim and fat PSPs.

It uses open standards, for maximum compatibility with other phone systems.
You can use a Go!Cam (Chotto Shot), Talkman microphone, or SOCOM-style headset for audio input. (And even if you don’t have any of those, you can still send audio from a WAV file in a pinch).
It’s still pretty much beta software – the audio quality needs some work (but it is usable), the UI isn’t very pretty, and video calls aren’t working (yet!). But it works, and it’s a nice demo of what is possible.

Since this is open source homebrew software, there are endless possibilities as to what inventive minds could do with this engine. We’d like to see a much nicer GUI (we suck at UIs!), and maybe a custom firmware plugin to use the engine as a teamspeak-style add-on feature for online games. Go on, go crazy and show us what you can do with it – you have our blessing!

http://www.noobz.eu/joomla/news/make-phone-calls-with-your-psp.html