I can't even think of good reasons why he may not continue the call. Because of his situation.. If anything I would think he would WANT to talk.. I would say maybe he is nervous to talk to you but I'm guessing you two have known each other too long for that to be a reason, idk I hope you actually get to talk to him !!
My husband does this. We don't get to talk too much because of money. So it's like hi baby I'm thinking of you. When he was in jail before we were married he was very jealous. It was the house phone and he wanted to check if I'm home. I cut that shit out quick. But now his calls go to my cell and I know he just wants to say hi. I always answer with I love you baby. And I get to hear that little snippet of hey baby. If they more than that can stop his calls because of getting 'free calls' or sending messages. I love to get to hear that little bit of him.
I was going to say the same thing... Sometimes my guy will call just to let me know he's thinking of me, even if there's no money on the phone or he knows I'm busy. And we've also had times where the prison's phones were messing up big time, and the call would disconnect as soon as I answered.
"It doesn't cost a thing to smile, you don't have to pay to laugh,
and you better thank God for that... there's hope!"