After connecting to our NEC SV8100 via the desktop suite, we can receive calls and hear callers but callers are not able to hear our voice. We're using the Desktop Suite 3.6 with a Plantronics CS50-USB. What should I check to diagnose this?

I assume your using SP310 softfone and perchance Win 7 64bit??

choose the phone view and turn the mic key on.

I just went through this exact same issue.

To trouble shoot I went into desktop config, made sure USB DEVICE was selected as my audio and recording source. Then after opening desktop/softphone I went into preferences and made sure USB device was set there as well.

Then choose the phone set view and click the mic key on the phone diagram.

D