try this, I will break down what i did step by step
1: on XOOM, go to settings>wireless & networks>tethering and portable hotspot and make sure that "Bluetooth Tethering" is UNCHECKED, this is NOT what we want
2: on XOOM, go to settings>wireless & networks> enable airplane mode
3: on XOOM, go to settings>wireless & networks> enable bluetooth
4: on your android phone, go to settings>wireless & networks (or equivalent)> enable bluetooth
5: Make sure that both devices are discoverable, so that they can see one another, should be in settings>wireless & networks>bluetooth settings
6: on XOOM, go to settings>wireless & networks>bluetooth settings>select your phone in order to pair it with your XOOM
7: a box should pop up on both devices, select Pair on both devices
8: on XOOM, once the pairing is complete (still inside bluetooth settings), select the phone, it should say paired but not connected underneath it
9: The two devices should connect, and if it works then the bottom right hand corner of your XOOM should have two bluetooth icons, one should indicated that your bluetooth is turned on and the other should say bluetooth tethered
10: TA-DA, if it worked then you are now using your phones internet data plan on your XOOM, aka not counting towards your xoom's data plan