A cell phone, especially one into which a person is talking in a loud voice.
"A few weeks ago, three members of Lil' Kim's posse stopped at a deli in Brooklyn, on the way to the airport. A guy inside was barking into his yell phone. The apprentice rappers asked him to talk more quietly. (And hey: If a rapper thinks you're too loud, you're too loud.) The man went on yelling."
Pete Hamill, "Condit least of our woes," Daily News, August 27, 2001
All New York voices, including the ya-ya voice, have been augmented by the yell phone, a/k/a the cell phone.
Richard Brookhiser, "Can We Talk?," National Review, July 12, 1999
This phrase will tickle the fancy of anyone who has been subjected to one side of an obnoxiously loud cell phone conversation. (Cell phone rule #37: The smaller the phone, the more likely a person is to holler into it.) Despite the fact that nincompoops have been shouting into their cell phones for about as long as these phones have been a plague on the land, the yell phone variation appears to be only a couple of years old, as shown by the earliest citation, below.
A shout out to Word Spy subscriber Shari Nadelman for letting me know about today's phrase.
In case you're wondering, the phrase ya-ya- voice used in the earliest citation is a coinage of Mr. Brookhiser's. Here's his explanation:
"Then there is the current rage, ... the speech pattern of young white women: the ya-ya voice. In cafes, shoe stores, bars, wherever two twenty-five-somethings gather together, or where even one has cornered a boyfriend, you hear the high, piercing patter: ya-ya-ya-ya-ya-ya-ya. If dogfish or other small sharks could speak, they would speak like this."