Thank you for asking this question in the support community. I believe what that statement is referring to is that when using the ADTRAN unit as a SIP Transparent Proxy, you do not have to use IP phones manufactured by ADTRAN. Here is the Configuring SIP Proxy in AOS guide for reference. I hope that makes sense, but please do not hesitate to reply to this post with any additional questions or information. I will be happy to help in any way I can.
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