You are partially right about this being a forbidden topic. There are a few places that you can find information on this. Google ESN Cloning or something like that.
a quick search brought us this link. It's for the 6900.
http://forum.xda-developers.com/showthread.php?t=380172
The most important thing to note on this subject is that it is illegal! Unquestionably illegal! There was a forum on here recently that showed how to put an MEID on the mogul and it went much more into the legalities. But to make a long story short if you get caught it's bad. If your ESN is on the network in 2 places on 2 phones your account will get flagged!
Although I'm not going to lie there is a certain thrill in just know that you are able to do something like this. So for fun you might want to know how, but it is unrecomended to break the law.