Your question isn't clear on where you sit in this silo'd group. If you are at the top, you have a bit more influence. That said, the techniques are going to be pretty much the same no matter where you sit.
You can't use role power to change something like this. So even if you are at the top, you can't just make it change. It is happening for a reason.
The first thing you need to do is understand why. Why does this culture of communication exist. The why is is critical. You have to define the present condition in detail. If you don't know where you are, you can't draw a map to where you want to go.
Next, look at your oganizational influences. Companies/People/Countries/Cultures/Groups have goals, values, priorities. These can have a major impact on your organization and effect how you make changes.
When you are done with this, then you understand where you are and what influences are impacting where you want to go. Now you can start going. I agree with edgaralgernon that meetings are a vital part of this. But they have to be the right meetings.
Meetings need to be effective and result oriented.
1- Define the purpose and goal of the meeting: A meeting invite with just a subject line is a meeting people are not incented to attend. You need to define what the purpose of the meeting is. You need to define what the high level outcome goal of the meeting is (a decision on test strategy for the Q3 release)
2- Agenda: You need a time boxed agenda published before the meeting. Then you need to post it. Time boxes should be clock based, not time based. At 1:00PM Meeting Starts, at 1:10 QA presents current status, At 1:15 we discuss options, At 1:40 we review options.
3- Understand the difference between a "Choice" and a "Decision." One of the biggest problems I've run into is this problem. Companies are really good at choosing a direction. They are horrible at deciding a direction. The difference? A decision defines "Who, What, When" Before leaving a meeting, you need to determine these three things and document them. Otherwise you just chose a direction, but it can be chosen again at the next meeting.
I recommend the Manager-Tools podcasts on "Effective Meetings" and "Making Decisions Effective."
Best, Joel BC