I recently signed up for services with Insight (owned by TWC), and was told while I'm permitted to bring my own modem, they require I take delivery of their "free" modem when service was installed. At the end of the signup process they required I agree to a 1 year commitment on the service. When I asked why this 1 year commitment was required, the response was "Because we're giving you a free modem".
Brilliant.