Using Blackberry data plan on iphone

[Kenal0]

I purchased an iphone used independance to jailbreak and activate using the att sim card from my Pearl which has the Blackberry unlimited plan.I use it for enterprise server and regular .mac account. I have an att corporate account. I called to make a few changes and told att that I occasionally take the sim card out and use it in my old razr if I do not want to take the Blackberry and can I add a data plan. The cs told me that I did not need it and my Blackberry plan would cover data from the razr browser. Anyone can confirm this? I do not want to get a crazy high bill for data usage on my account because of mis information.
Thanks
Kenal0