It's called spoofing.

by R. Proffitt Moderator - 12/14/12 8:06 PM

In Reply to: text message cloning by blazebd

I'm not going to detail anything about it except it's name. Sorry but why should I help propagate how?

Here's a CNET article for your research.
http://news.cnet.com/8301-17938_105-57496786-1/iphone-sms-spoofing-tool-surfaces/

Bob