Can he take advantage of a mistake by the phone company to make calls for free?
Question

                A few weeks ago, a Pakistani cell phone company allowed phone calls to Palestine, but the problem is that when you made a call, no money was deducted from your account and it was possible to speak for as long as you wanted, even ten hours, without paying any money. Is this permissible or not?.
Praise be to Allah.What you 
    mention has to do with a technical error made by the company. The basic 
    principle is that it isn’t permissible to take the wealth of a Muslim 
    without his consent. So long as the company has not announced that it would 
    overlook this mistake, it is not permissible to take advantage of it. Rather 
    you should have contacted the company and told them about it. The Prophet 
     (peace and blessings of Allaah be upon him) said: “No one of you 
    believes until he loves for his brother what he loves for himself.” Narrated 
    by al-Bukhaari (13) and Muslim (45). 
And Allaah 
    knows best.