How do online services provide unlock codes?

[Guest jblz]

First off, I've only ever one of these services once but it worked perfectly. Since then I've either been able to unlock the phone myself, or I bring it to a guy in my city who has a lot of serious looking cables.

How do online unlock code vendors provide unlock codes? I've pondered this for years

I've come up with a couple possibilities;

They call up network operators posing as someone who travels a lot etc and obtains the code that way. With a large volume or orders I can't see this happening, plus many of these places offer instant unlocking so this wouldn't really be possible.

They've figured out whatever algorithm is used to convert an IMEI to unlock code. Is this the same between different operators? Did they find some leaked info?

I don't know if a handsets unlock code will always be same even if the IMEI is changed. Perhaps people are changing the IMEI on their own handset and the new unlock code is generated by the phone? (on a handset where unlocking and changing IMEI is easily possible)

Anyone have any knowledge? It's driving me nuts.

Edited February 24, 2012 by jblz