用户可以一直在线，按照用户接收和发送数据包的数量来收取费用，没有数据流量的传递时，用户即使挂在网上，也是不收费的。
我们没几个人会自己发电：我们依靠联营的电网，按需使用，按量计费。
Few of us generate our own electricity: instead we rely on the pooled resources of an electric grid, use what we need and pay by the meter.
利用GPRS系统“永远在线”、“按量计费”等优点，研发了远程无线监测热工仪表系统。
The remote wireless system for monitoring thermal meters based on GPRS was developed due to its good features of always-online and charge-by-byte etc.
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