300卡业务是中国电信记帐业务。拥有300卡的用户可在国内任何一部双音频电话机上拨通300850及帐号、密码等30余位号码后,即可任意拨号使用,通话费在卡(帐号)上自动扣除。使用300卡业务不记长途、农话附加费,可节省话费,但是需拨30多位数字,不易记忆和操作,特别是当一部电话或一卡多人使用时会感到很不方便。本文介绍的300电话拨号管 300 card business is China Telecom billing business. Users with 300 cards can dial 300850 and more than 30 numbers, such as account number and password, on any dual-tone telephone in China to dial any number. The call charge is automatically deducted from the card (account number). However, dialing more than 30 digits is not easy to memorize and manipulate, especially when using a phone or a multi-card phone. This article describes the 300 telephone dial-up pipe