As expected, Best Buy is having an in-store fire sale today, Monday August 22 only, on the 8 GB iPhone 3GS. The 3GS is available for free which is the perfect price for someone who absolutely wants an iPhone, but doesn't want to pay up front for a handset.
Be aware that this deal requires a two-year customer agreement with a $325 termination fee and a monthly data charge, so there are some hidden costs associated with this free handset. If you're not ready to commit to the 3GS for two years, you can always check out Auntie's advice on finding a low-cost, off-contract iPhone 3GS and pairing it with a cheap PAYG plan with data.
And yes, the 3GS is a two-year old model, but it's still a worthy handset. It sings along on iOS 4 and can handle iOS 5 just fine. There are some limitations, like no FaceTime support, but it's perfect for the budget conscious consumer looking to experience the iOS platform with minimal cost.