AT&T has lowered the cost of its unlimited voice + data iPhone plans. The price of the individual unlimited voice and data plan for iPhone users has been lowered from $130 per month to $100, while unlimited Family Talk plans that include two iPhones have been lowered to $180. Unlimited texting remains a $20 for individuals or $30 for Family Talk plans. Current customers can change to the new, lower-priced plans without incurring a penalty or contract…