Is it illegal to unlock a locked phone?

Could you please clarify for me, is it considered illegal to unlock a phone that has been locked? I'm genuinely curious about the legality of this action and would like to understand the consequences, if any, that might arise from doing so. Could you elaborate on the relevant laws or regulations that might govern this matter? I'm interested in learning more about the legal framework surrounding phone unlocking and whether it differs depending on the context or the method used for unlocking. Thank you for your assistance in clarifying this matter for me.