Koko was complaining on one side on the phone while on the other side, Inui was doing the same. They were your friends before you even started dating and they 'forced' you to have two cell phones, because they always came to complain about each other and as friends with both of them, you needed to intervene.

Kokonoi: Seriously, he's being very demanding. Can I no longer have male friends?

Inui: He's an idiot. I've said a thousand times that that friend of his has other intentions.