Obtaining a PUK is usually remarkably simple - in fact for some providers it merely requires the phone number to be submitted to their website. That never seems very secure to me. Alternatively I have had them over an automated phone call as well. Not sure whether you are country-specific but the Zain (Kenya) website has these answers:
Q: My phone says PUK. What does it mean?
A: PUK is an abbreviation for PIN Unblocking Key. Your phone will display this message if a wrong PIN number has been entered more than three times. Take your phone to any Zain outlet and they will unblock it for you.
Q: Where do I get a sim replacement?
A: Get a free swap replacement at the nearest Zain center
Doesn't say whether they can recover the memory. Best to store contacts on the phone I guess, then they are useable with any sim.
According to the O2 website, for Nokia you get 2 messages:
For 'Simcard blocked - Enter PUK', you need a PUK,
for 'Simcard rejected' you need a new sim.