Hmmm.  Well, the numbers you assign for use as Meet Me lines (MML) are not limited in anyway.  You can configure as many numbers as you wish. Which is the answer to your question.

That being said, you do need to ensure you have adequate media resources in either hardware or software.  The media resources available to you will depend on what hardware and/or software you have in play.  If we are talking about simple software conference media running on the CUCM system, the default limit is 48 streams per IPVMS node in the cluster.  Of course, these streams aren't pooled so you have to keep that in mind too.

Within a MML bridge, you can set the maximum MML participants in a single conference usign a service parameter.  The default value is 4 per conference.  You can increase this, but (again) you need to consider your available hardware and software resources and how they are allocated to devices/users.

HTH.

Regards,
Bill

Please remember to rate helpful posts using the stars below.

You don't have to use DID for MML's; however, if you use a private extension range - those conferences will only be available to internal users.

As for the number of participants, this depends on the capabilities of the software/hardware  conference bridge.  For example, a software conference bridge supports up to 128 participants.  There is a service parameter to limit these parameters as well.  For more information on that, see https://supportforums.cisco.com/message/1169918;jsessionid=6600552C836585353998DC8294207314.node0.

Hailey

Please rate helpful posts!