As luck would have it, this exact issue is mentioned in chapter 1 of the FreeSWITCH Cookbook in the recipe entitled, "Advanced multiple endpoint routing with enterprise originate." While you click here and pre-order your copy ;) I will give you the synopsis:

You MUST ignore early media when doing an enterprise originate. Therefore, to get ringback tone you'll need to set the ringback channel variable on the A leg. Your extension will end up looking something like this:

<action application="set" data="ringback=${us-ring}"/>
<action application="bridge" data="<ignore_early_media=true>[leg_timeout=0][origination_caller_id_number=30]user/35@${domain_name}:_:[leg_timeout=0][origination_caller_id_number=30]user/31@${domain_name}"/>

Note: when doing any kind of multiple endpoint originate, whether using the enterprise originate or just the comma-separated list of endpoints, it is 99.99% of the time necessary to ignore early media. Why? The answer to that question is eloquently stated in both chapters 5 and 8 of the first FreeSWITCH book. Check it out. :)

-MC

On Wed, Feb 15, 2012 at 9:37 AM, Christian Benke <benkokakao@gmail.com> wrote:

Hello!

I have a question about ringback-tone when calling multiple
destinations. When i call a single directory-user, i get a proper
ringback-tone - but when i add a second user to the bridge-command,
there's no more ringback-tone.

This is not about early-media - the phones only send 180 Ringing and
the ringtone is provided by FS.

Shouldn't FS send a ringback-tone as soon as the first phone answers
with 180? Or is this behaviour just as intended?

I've attached sip-traces of both situations plus the respective extension.

Best regards
Christian