asterisk users - May 2008 - Listen And Talk mode differentiation of meetme() conference

Hello users,

i am trying to setup a conference system
and i  have following requirement

1)some users are only in listen mode
2)some users are only in talk mode
3)some users are able to do both talk and listen

how to diffrentiate them when they enter into a particular mode?
meaning do i have to give a separate access number in my extensions.conf file
so that i will bridge them all together in once coference using meetme() or
is there any separate way to do that

my idea is like this one

1)all listen only users can call on 123

   exten => 123,1,MeetMe(9999|Mm)
   exten => 123,2,Hangup()

 2)all talkers can call on 456

   exten => 456,1,MeetMe(9999|Mt)
   exten => 456,2,Hangup()

3)both talk and listen users can call on 789

  exten => 789,1,MeetMe(9999|M)
  exten => 789,2,Hangup()

does this setup only works?
or is there any other method of doing the things

just enlighten me so that i can finalize my setup

thanks in advance
regards
srinvias antarvedi