Why would hardcore libertarians defend laws like these? It's an obvious market restriction.
However the government should not have the power to actually grant this.
I suppose a hardcore libertarian might allow a contract clause which allows the phone network to hire someone to shoot you in the face if you unlock your phone.
But yeah I think your interpretation is correct.
That's not been my experience. Organizations like reason.com and the Cato Institute regularly criticize businesses that use government regulations to stifle competition and restrict the rights of customers. A solid majority of libertarians support either eliminating or substantially weakening IP laws. (There is a minority that believes that IP be treated the same as physical property, with infinite copyright terms and other silliness).