Is it unlawful in Islamic law for a sister's husband to call his sister-in-law on her mobile phone if the call does not exceed one minute and is only to check on her well-being?

It is permissible for a woman to speak with her sister's husband when there is a need, provided certain conditions are met: that the speech is free from softness that could lead to temptation, and that there is no pleasure derived from the other person's voice. Otherwise, speech between them becomes forbidden. Out of piety, it is better to avoid it, for the Prophet, peace and blessings be upon him, said: "Leave that which makes you doubt for that which does not make you doubt." If the husband objects to this conversation, it is obligatory to abandon it in obedience to him in what is good.