If you choose to deploy a SPA400 in an Asterisk environment, you will need to define which SPA400 line to use.
This document describes how to accomplish this.
exten => 6XXXXXXXX,1,Dial(SIP/L2{EXTEN},20)
By setting Ln string before an extension in the INVITE, where "n" is the line number on the SPA400, one can choose which line to route the call to (in the previous example it goes to Line 2). If not using Ln, the call will end up on first available line (the SPA400 is then treated like a trunk). This has been tested to work with 1.1.2.2 SPA400 firwmare.
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Special thanks to Ognjen Seslija for sharing this information with the community
