User agents are typically phones (POTS, mobile phones, soft phones, IP-PBX devices, and so on), but can be any SIP-enabled device.

用户代理一般是电话(POTS、移动电话、软件电话、IP - PB X设备，等等)，但可以是任意的允许SIP的设备。

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I've been looking around for a "commercially supported cloud-based VOIP PBX that provides dial tone" for the past few weeks and I keep coming up empty on the SIP phones.

在过去的几周里，我四处在寻觅着一个“商业支撑下、基于云的并可提供拨号音的网络电话交换机”，而一直无法享用SIP电话。

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SIP Trunk is a logical connection between an IP PBX and a Service Provider's application servers that allows voice over IP traffic to be exchanged between the two.

一个SIP中继是一个IP PBX和服务提供商的应用服务器，使语音的逻辑联系IP流量将两者之间的交换。

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