Help jailbroke iphone 4 - inserted different carrier sim card and now No Service?

I bought an iphone 4 that was jailbroke using straight talk. I got my sim from simple mobile cut to micro put it in and No Service. I have cut it on and off on and off - still No Service. Any advice? Do I have to start using Straight Talk?

SIMple Mobile and Straight Talk are two different things, if you do not have service with SIMple Mobile, then that is the issue.