Access the SPA3102's web-based setup page. For instructions, click here.
When the SPA3102's web-based setup page appears, click Voice.
Under Preferred Coder, select G.711U.
Under Voice Coder, set all VAD to ON.
Perform a power cycle.
Note: It will also be helpful if you set the SPA400 on the WAN side of the SPA9000 and make sure that Proxy Network Interface is set to WAN. This can be found under the SIP tab of the SPA9000.