Nagato's spoken before in this comic. She just says her name over and over, like a Pokemon. We don't see any dialog from her here, so I can only presume that that's what she's doing on the mic.
Just read through this whole pool, and Nagato never says anything outside her signs. There is one speech bubble with her name in it close to her head at one point, but its tail is pointed to Kongo.
Wokyu~!Hey, she's calling for you, so go to her!They're playing KanColle anime make-believe, they say.Bannng!G'shakSay, ain't that your eldest sister?Hey, that's your eldest sister, ain't it?PaffTh-...thank you very much...KanColle Anime Episode 1!!Love!Uuuuh...Kirishima! Kirishima!!I get the feeling there's some quite grown-up folk joining in on this make-believe...