Green’s Dictionary of Slang

(US black) a (public) telephone.

1995		L. Stavsky et al. A2Z 55/2: jack – 2. n. telephone.
1998		Big L ‘Ebonics’ 🎵 Also, cribs is homes, jacks is pay phones.
2011		G. Hayward Corruption Officer [ebk] cap. 54: After lunch we all talked on the ‘jack’ to one another since our cells were right across from each other. Talking on the jack is another name for telephone, consists of us laying on the floor and talking to each other through the bottom of our cell doors, due to the fact that they were elevated.
2012		‘Dutch’ ? (Pronounced Que) [ebook] He talked to you on a federal jack?