Ah, the thrills of a handset-still-in-development. It's been months since I had that... but this is mine, and it's a sonyericsson, not a pre-production Panasonic!
Basically, on the latest P990i software version, the phone app gets confused if you've got contacts which are in both the SIM and the handset phonebooks, and as a result personalised ringtones, number to name lookup etc don't work.
Simple solution - delete all the contacts on your SIM. It's not as if the phone uses them anyway...
I only stuck that on here so Google'd index it and some other poor sap will be able to find this solution pronto. Only one problem though... how do you access your SIM phonebook on the P990i...? I used an old Panasonic GD96!