Hi there, if u are using Null subsystem for ur session management, then u need to connect to ur dedicated server with IP address, u just need to create local session, then join the dedicated session with IP, thats all. the voice system only need session info to work.
so if u create session localy and find the session and join with the session, the voice will work, but if u host the session on dedicated and its not loca, then u cant find that session and join it with session, so u need to join it with IP, if u join with ip that means u dont have session info, so before joining with IP, u just need to create fake local session.
I hope i said it good, Good Luck