Member rivvah from HowardForums has posted a comprehensive list of s60v3 product codes for various Series60 3rd edition phone models. For example, my N91’s code is:

N91 RM-43
0535291: English, Chinese

The part “RM-43″ can be obtained by pressing *#0000# on your S60 phone. The number “0535291″ can be found under the battery. The languages can be found in the Menu under Tools->Settings->Phone-> General.

This guide serves as a great resource for people who buy unlocked phones from retailers which sell imported phones. It allows a person to verify if the phone given to him has the correct firmware or if its firmware has been changed/modified. For example, A Nokia E50 RM-170 with a product code of 0534465 must be an Indian BLACK edition. So if you find a phone with that product code, but different languages in it, you can be sure its firmware has been modified. Please do note that though the list is fairly extensive, it is not complete. The N91 code I posted above is not on that list. However, it is a great resource, definitely bookmarked for future use.