Well, I do not know who will enforce this but if you go strictly by the terms and conditions you agreed to with AT&T, you can not really call into a conference call with your iPhone if you have unlimited voice services. From the AT&T iPhone terms and conditions: Unlimited Voice Services: Unlimited voice services are provided solely for live dialog between two individuals. Unlimited voice services may not be used for conference calling, call forwarding, monitoring services, data transmissions, transmission of broadcasts, transmission of recorded material, or other connections which do not consist of uninterrupted live dialog between two individuals. If AT&T finds that you are using an unlimited voice service offering for other than live dialog between two individuals, AT&T may, at its option, terminate your service or change your plan to one with no unlimited usage components. AT&T will provide notice that it intends to take any of the above actions, and you may terminate the agreement.