Can I activate an iPhone without 3g Service?

I recently (accidentally) reset my iPhone, and it was working fine with no SIM previously. Now, however, I'm attempting to use it again, and it tells me that I need to activate it with a SIM card. I have a working SIM, but don't want to use it because I'm worried it will add 3g to my plan. I can't afford it. I only want to use my iPhone for Wi-Fi and music, I have no plans on using it as a phone. And it won't work by just "Turning it on", because It says it needs to be activated.

Alternatively, if I put the SIM in, activate it, and take it out, will it add 3g or not?

Bottom line, I don't want to be charged.

Activate and cancel your service, and the Wi-Fi functions still work:

Per AT&T's terms of service: If you cancel your AT&T service within 30 days you do not have to pay an early termination fee; and if you cancel within 3 days you get a refund of your activation fee. No guarantees that it will work.