Can you put any AT&T sim in an iPhone?

[durat33]

Recently, I bought a cell phone (a Pantech Link II), without a data plan. Since it was new I obvoiusly recieved a new SIM with it.
Here's my idea: My dad's old iphone 3 (not 3gs, just 3g) is still functional (I actually use it as an Ipod). Can I put the SIM from my new phone into the iphone?
I know that I physically can put it in (in fact, I already have. The iphone gives me a notification that the phone is activated).
I was just wondering if this is legal and what not. I'm not using data, of course, bc that was not paid for with my plan and I don't want extra charges. Will AT&T force me to buy a data plan, or will I be able to use the iPhone for texting and calling only?

[BRIAN2]

From what I recall, someone told me if you don't launch the browser on smartphone, att won't force you to get a data plan. 

[Facci]

If you are using an iPhone, you have to have a data plan on your plan. If you don't have it AT&T WILL add one to your account. They can tell just from the IEMI on the phone. It happened to me a couple years ago.

[graphite07]

Data is a required for the Iphone.

[renewedpurpose]

Yes, you can physically place your SIM card in the iPhone 3G. Keep in mind that all smart phones, including the iPhone, require a data plan. AT&T can detect the IMEI of the phone you are using and once they catch you using a smart phone without a data plan they will automatically add one for you.