How many devices can I connect / tether with iPhone Personal Hotspot?
Multiple devices can share your cellular data connection if the Personal Hotspot feature is activated as part of your carrier data plan. The Verizon iPhone 4 running iOS 4.2.6 or later and the iPhone 3GS and iPhone 4 on AT&T running iOS 4.3 or later support Personal Hotspot.
The maximum number of simultaneous devices that can be connected via Personal Hotpot on the iPhone 3GS is two. One connection via USB and one connection via Bluetooth can be used at the same time.
On the iPhone 4, a combination of available Bluetooth, Wi-Fi or USB connections can be made for a maximum of five simultaneous devices connected. The AT&T iPhone 4 supports up to three Wi-Fi connections, three Bluetooth connections, and one USB tether. The Verizon iPhone 4 supports up to five Wi-Fi connections, three Bluetooth connections, and one USB tether.