The Fring blog has announced, in a low key way, that its VoIP and chat freeware is now compatible with the Sony Ericsson P990i (but not the W950 or M600). You'll need the latest P990 firmware, but I'm sure you have that already?

"You can get fring on your Sony Ericsson P990i in 3 steps:

1. Check that you have the latest firmware. (Go to Main Menu / System Information. The latest firmware is R6D23). If you don’t have it, get it from Sony Ericsson. Go grab a cup of coffee - it will take about 15 minutes to install.
2. Get an audio plug-in from fring here (takes about 5 seconds)
3. Get fring via SMS as usual (fring should be up & running within about a minute as usual)"