FoxFi Software has FoxFi Wireless HotSpot / Tethering App for Android in Google Play (formerly the Android Marketplace) for FREE for a limited time.

Enables WiFi or Bluetooth Hotspot on your Android phone without a Hotspot plan from your carrier. No rooting required! Just install and turn it on. Bluetooth mode works for all phones. WiFi mode currently works on most Samsung phones and Motorola phones. WiFi mode does NOT work on any HTC phones or the first Motorola Droid/Triumph, use Bluetooth mode instead.

You can connect from any tablets or computers. Access Point is infrastructure mode with WPA2 security. FoxFi usage is covered under the same phone data plan you have.