No call waiting, callers sent directly to voicemail

[spalten]

I seem to be having a problem with my EVO. When someone calls me when I am on a call aready, instead of me getting a call waiting notification the user is sent directly to my voicemail. Any suggestions on how to fix this?

One point that maybe important, is I setup my google voice account to take the voicemail on my phone. Does that have anything to do with it?

Any help you can give would be great.

Thanks!