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I am afraid that this is governed by the terms of the contract you signed with Sprint. You need to review that contract, since it does contain a clause about return of equipment within a certain period of time and failure to do so is breach of contract which entitles them to recover the damages that are specified in the contract, equipment costs. Legally, this is indeed a breach of contract and you would have to call and negotiate with supervisors (not the lowly customer service people) to arrange for a return of the equipment in exchange for them clearing the charges from your account, but if they refuse to agree as it is outside of the contractual return period you agreed upon, I am afraid it is legal for them to pursue you for the costs of the equipment pursuant to the contract you signed.
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