I'm sorry, I have the same question, but I don't quite understand the answer you've given.
I have a 3GS updated to 4.2.1, and I jailbroke it today using redsnow. I didn't unlock it and I don't need to. I have a monthly cell phone plan, and I got a sim card as part of that package. Should I be worried about this Hacktivation business?
If it's constantly using my dataplan, am I going to get charged a bazillion dollars?