In addition to the HP TouchPad sale mayhem, Best Buy is giving away free 8GB Apple iPhone3GS Monday in stores only for new two-year AT&T contract signers, hinting the forthcoming iPhone 5 release date.

The fine print: In order to receive the free iPhone 3GS, consumers must sign up for a two-year contract with AT&T in stores only, as the offer is not available online and only is available on Aug. 22.

Best Buy shoppers must sign a new two-year activation contract or renew a contract due for upgrade for two-more years in order to be eligible for the free iPhone.

According to CNet, this giveaway of Apple iPhone 3GS can double the current amount of iPhone users worldwide, estimated at 64 million, to over 150 million.

The giveaway also bolsters rumors regarding the iPhone 5 release date, rumored to be an Oct. 7 launch with preorders beginning on Sept. 30, as reported by 9To5Mac.

The offer, announced today by Best Buy Mobile in a new Deal of the Day campaign, will only last today, Aug. 22.