We received a lot of questions and conflicting reports about whether or not the new iOS 4.3 personal hotspot feature would work on iPhone 3GS and the answer -- from a software standpoint as of beta 2 -- is... kinda.
Personal hotspot replaces tethering in the iOS 4.3 Settings system and while iPhone 3GS does indeed show the new Personal Hotspot feature it doesn't show the Wi-Fi option available on iPhone 4. Yup, Bluetooth and USB are the only options, same as were previously available under Tethering.
Now whether or not Apple adds the feature in for iPhone 3GS users when iOS 4.3 goes into general release, and whether individual carriers like AT&T choose to implement it or not we don't know. But as of now, there is Personal Hotspot, just no Wi-Fi, and that means 1 device only, not 5.
For more see our iOS 4.3 walkthrough.
UPDATE: Per comments below, no Wi-Fi option for iPhone 3GS under iOS 4.3 beta 2.