(Phone) busy—used to indicate that a telephone line is currently engaged in another call.
ごめん、今その番号は話し中だから後でかけ直して。
Sorry, that number is busy right now, so call back later.
留守番電話には『話し中』の案内が流れていた。
The answering machine played a message saying the line was busy.
お店の予約ダイヤルは話し中が続いている。
The restaurant's reservation line continues to be busy.
Under discussion; in talks—indicating that something is currently being discussed or negotiated.
その案件は現在社内で話し中なので、詳しいことはまだ言えない。
That matter is currently under discussion within the company, so I can't give details yet.
私語で席を立たないでください。今は話し中です。
Please don't get up to chat. A discussion is in progress now.
両国は条約の内容について話し中だと報じられた。
It was reported that the two countries are in talks about the treaty's terms.