I was not able to get this working. I'm using an Evo 4G on Sprint running Gingerbread 2.3.5., and an Asus Transformer TF101 running ICS 4.0.3. Both devices indicate that they're paired, and on the Evo, a screen pops up asking for permission to allow the Asus to connect, but after allowing, it never connects. One of the other posters in this thread mentioned that Sprint had disabled this type of functionality. So, either that is true, or I can't follow these simple instructions properly (g).
I also tried the FoxFi and PDA Net Tablet combo, but this failed also based on the following help file entry from FoxFi:
*the Asus Transformer/Prime version of ICS firmware is missing the "tun.ko" component which is required for our Bluetooth Internet solution to work properly. So this particular tablet is not supported UNLESS you root the system and install "tun.ko" manually (google for details).
ICS is a tough one you will have to do a Wi-Fi tether because even though it has a bluetooth tether option it was not FULLY implemented so you need a helper app to proxy the data to and from the bluetooth connection and it only works with like Firefox browser [with an added extension needed].
Best option: JELLYBEAN! Once I updated both phone and tablet to JB [phone in a Tmo S2 technically still no JB from them, but fully stable JB still available so look at custom ROM if needed my tab is a Nexus 7 so yeah it has JB. I use ParanooidAndroid on both devices.
In JB it is super easy go to settings and more and tethering and tap to check bluetooth tether [this turns off at every boot so re-enable after every restart or your other device fails to connect until it is enabled again]/
On phone enable bluetooth tether as above
Open settings>Bluetooth
Tap to make discoverable
On Tablet open and turn on bluetooth
now tap search devices [in upper right corner of screen]
once it finds the phone tap to pair
On Phone:
Accept the pair request
NOW once they are paired everytime you need tether
Open setings>More>Bluetooth tether>Tap to enable bluetooth tether [it gets turned off after EVERY system boot [some apps help turn this back on auto but some cause issues so I do it manuallyt]
Anyways on tablet once the bluetooth has been turned on on the phone and tabllet... click the icon to the left of the phone entry in bluetooth list. This will bring up a second screen with a listing that says use this devices connection to get on the internet [or VERY close] tap that specifically so a check appears and you will see a connecting... prompt. Once done you can now use data on your tablet
ONLY NOTE: VERY FEW APPS are porly coded to check specifically for a WiFi or Cell Dta connection and if non-found to throw an error. MOST Android apps [I LOVE NETFLIX TABLET VIEW THIS WAY WHEN ON THE ROAD FOR INSTANCE] Will not care and function as they always have/
Your tablet may still say not connected [where it usually says the name of currently connected WiFi network]. This is actually LYING try using a browser to get to google to truly verify this
ALSO: it may take a few seconds after you tap the connect on tablet and truly have full data access be patient
LAST: if your data drops in and out and you have to restart the phone to get it back, you may need to check your screen off CPU Max setting and increase it, if the CPU is not moving fast enough bluetooth connection will most likely malfunction until device is restarted.