Is using proxies to connect to the Internet for free, without paying subscription fees to wireless telephone companies, considered an infringement on the rights of these companies? And what is the ruling of Islamic law on that?

It is not permissible to resort to deception to evade paying the prescribed internet service fees, because it is the property of others, and it is not permissible to benefit from it without the consent of its owners, as Allah Almighty says: "O you who have believed, do not consume one another's wealth unjustly but only [in lawful] business by mutual consent." Repentance is obligatory, and one must discharge oneself from what was consumed unlawfully by paying its value to its owners before the Day of Resurrection.