No data should be lost on the sim or the phone.
This is just a block that is put on the phone when, like you say, some one enters the pin wrong 3 times or more.
Enter the PUK Wrong 3 times usually leads to SimCardBlock which like has been said renders it useless.
Either way, phone data is not lost. And if you cant get the PUK then a Sim card reader will recover data from the simcard.