Depends on which phone and whether you have a phone-as-modem (PAM) plan. With sprint or verizon, if you don't have a PAM plan, you'll need usbmodem or pdanet. If you do have a PAM plan, you can use BT-PAN, otherwise, with usbmodem/PDAnet, you'll need BT-DUN. I have BT-DUN working with a moto Q9c and PDAnet.

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