Definition of: ISDN (Integrated Services digital Network) an international standard for switched, digital dial-up telephone service for voice and data.

定义：ISDN(综合服务数字网络)，是一个国际转换标准，是为了语音和数据的数码拨号上网电话服务。

youdao

As more voice minutes are switched to the Internet and traditional telecoms firms react, marketing and service costs are likely to rise, narrowing the price-gap over time.

ECONOMIST: Internet telephony