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i use iTether on my JBed iPhone, so that iPad can get online using bluetooth connection to iPhone. works great.
 
Connecting non-3G iPad to iPhone (leveraging 3G connection)

I've tried this and it definitely works. What you need: iPhone, iPad and MyWi installed on your (jailbroken) iPhone. I don't believe you need to jailbreak your iPad to make this work, but haven't verified it as my iPad is jailbroken.

Steps.

On iPhone:
- Download MyWi from Cydia. You only need this on your iPhone.
- Open MyWi, tap the bluetooth icon
- Turn on bluetooth tethering

On iPad:
- Go to Settings -> Bluetooth
- Toggle "On"
- Under Devices, you should see your iphone
- Tap on it
- To confirm on BOTH devices, tap "Pair".

And you're done. You will now see a different icon next to the word "iPAD" that looks like two rings intertwined.
 
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