I use italics for texts and in my latest book (WW2 Era) letters. Conversations via phone or skype I treat as normal dialogue, just add some details to make sure the reader knows how they are communicating and make it realistic
Cellphone:
"What?" Jack said. "I couldn't hear that."
Skype:
"Okay," Jill said. She wanted to reach through the screen and touch him, but she couldn't, he was 3000 miles away. She couldn't believe she wouldn't see him for another two weeks.
I've done TV and radio the same way. I think I used Italics for song lyrics coming out of the radio once, (don't worry I wrote the lyrics) but the DJ was in quotes. Maybe that was completely wrong, I'm not sure. I think the most important thing is that it is clear to the reader who is talking.
Helena sat on the couch and grabbed a slice of pizza. No one said anything to her, she didn't even get a nod. Everyone focused on the TV.
"I had never seen anything like this," said the witness.
"Could you describe it?" asked the journalist.
"It was like looking at the devil's face."
Helena got a chill and spilled the coke on the floor.
Honestly without you explaining that it was on TV, outside of the text, I don't know if I would have known where the witness and journalist were, sorry.