It has been rumored but the day is here, Apple has started selling the iPhone 4 unlocked, supported by GSM networks. The outright 16GB versions retails for $649 while the outright 32GB model sells for $749. Outright, no contracts. Both black and white models are available and include free shipping from the Apple Store only.
Right now the black model has an estimated shipping time of 1-3 business days whilst the white model amps it up to 3-5 business days. Apple will ship the iphone 4 without a micro-SIM card, but "requires an active micro-SIM card that you obtain from a supported GSM wireless carrier."
Apple have done this for customers who don't want to be on contract or for overseas travellers. There is a drawback, because of 3G incompatibilities, the iPhone 4 will only work over the T-Mobile EDGE (2G) network, this limits the data transmission speed of the phone. The upcoming iPhone 4S/5 is reportedly going to receive "global" 3G radio which allows it to operate on CDMA networks and a wider range of 3G GSM networks.