Yellular is the loudness one adopts in response to a bad cell-phone connection, in the misguided hope that talking louder will improve the connection.
这个yellular其实就是yell(喊叫)和cellular的合成词，我们的手机正式叫法是cellular phone(蜂窝电话)，简称cell phone。
Sometimes, some people just cannot help yelling whenever they are on the phone, it seems that their voice is not transmitted through phone signal but via a speaker.
I'm so embarrassed. I went totally yellular at a restaurant last night. I was talking to my dad on the phone, but he just couldn't hear me no matter how loudly I spoke on this side.