Some might know that older Nokias have longer mastercode which can be calculated from IMEI code and it works even though the default 12345 is changed to something else. Basically there's two codes which works. There's plenty of calculators, few to mention: http://mastercode.nokiafree.org/ and http://nfader.su/ (compatibility for both: http://nfader.su/forum/viewtopic.php?t=12)
Basically same models reveal their current security code via data cable using LogoManager or similar. Start the program, plug in the cable, turn on the phone and program knows the code.
Certain Nokias, like 2110, doesn't have 12345 by default because it's calculated from IMEI and printed to the box it came in. However, if previous owners had changed it, game over -- 2110 has just one code. There's a 16-bit DOS app sid.exe for this.
Many newer Nokias resets its security code reset back to 12345 when software is updated and no backup is created/restored. This requires cables though.
How about other manufacturers? Point is to gather instructions to open legally owned phones, not stolen ones -- even though most of our phones are old (and worthless to most people ). What is more disappointing than finding a new phone to your collection, but after charging and cleaning, it wants a security code?
If finding a security code requires a data cable, fine, but if anyone knows tips or tricks to get locked phones opened without buying anything (I presume everyone has access to a computer and Internet), please post.
I have a Ericsson T28s which asked the code, but luckily previous owner had written it down to the user manual. Now I have a Siemens M50 which asks the code and apparently I have one attempt left, thanks to previous owner...