Wiktionary
sex line
n. A phoneline reserved for phone sex.
Usage examples of "sex line".
I figured with the no-sex line you just drew in the sanduh, linoleumthis would be my last chance.
Nina wondered why the guys who phoned the sex line never sounded like that.
Four have phone-solicitation businessesone also runs a phone sex line, by the waytwo have pulpits in churches with shaky charters, and one is wanted by the Feds, something to do with mail fraud.