[tsteffens]

I have the full version of 3cx installed and everything works great with yealink t28p. I am now playing around with the 3CXPhone softphone for windows and it appears if I leave a message it doesn't trigger the MWI or the little envelope doesn't light up.

Any suggestions?

[leejor]

If you have a SIP phone, with the same extension number as the 3CX Phone, does the MWI light on that set?

[tsteffens]

If you have a SIP phone, with the same extension number as the 3CX Phone, does the MWI light on that set?

Yes, this does work as expected when the softphone is programmed as the same extension as my sip phone.

[leejor]

Does the 3CX phone show a missed call?

[tsteffens]

yes, shows every missed call.

[leejor]

Had a netbook with an older 3CX phone on it (Ver 4.0.9157.0) , tested MWI, worked as expected. Downloaded the latest version (6.0.19920.0), installed and configured (basic settings, just enough to place a call), again it worked just fine.

Your problem could be one of three issues..
(1) possible software corruption?. Unlikely, but perhaps try a complete un-install and re-install of the softphone.
(2) for some reason the MWI is not being sent, Wireshark could confirm this.
(3) MWI is sent but not reaching the PC running the phone (network issue?), perhaps a firewall on the PC is blocking the message. Again Wireshark would show if the message is indeed reaching the PC but the 3CX phone is just not acknowledging it.