Rogers Wireless has announced a set of iPhone 3G S discounts that it will offer to certain prior iPhone customers. For customers who bought an iPhone 3G between July 11 and Sept. 30, 2008, and with an average monthly spend of at least $100, Rogers is cutting $500 off the cost of an iPhone 3G S, bringing the prices down to $199 and $299 for the 16GB and 32GB models, respectively. For customers that bought an iPhone between July 11 and Dec. 31 2008…