Unable to do 3 party conference on my 3300

[PokerMunkee]

I believe this started happening after we switched from PRI to SIP for all external calling.

Happens on 6920 and 6940 phones.  I call my cell.  I then click "Add User" and dial the 3rd person, which connects fine.  Then I click the "Join Calls" button.  Nothing happens.  I'm still talking with the 3rd person. 

Any ideas where to look?

[PokerMunkee]

Figured it out.
 System Options, there are 3 settings for max number of C.O Trunks, devices and Trunks allowed in a Conference.   Set all to 5.  CO Trunks was set to 1.

[ZuluAlpha]

Great find! Makes me wonder how it ever worked before!