When being asked a question you don't know the answer to, the question falls into three categories.
A question you really should know the answer to.
Something that is totally inside your purview, and you should have been prepared for. For example, "When will you have X project done?" when your the lead on that project.
Your best bet in this case is to guess, and guess correctly. Then hold your self or your team to the answer. Again these are questions you should know the answer to.
A question that someone else should know.
These are questions that should be deflected to someone else. For example, "When will other team have project X done?" Your best course of action in this case is to suggest that it's not really your area but that you could look into it. "That's Bob's project but I can take a look if you want." In most cases, the asker just doesn't realize that it's not your question. You need to be careful, your not trying to "push blame" or take over. Your just trying to inform the people there, that it's not your issue. In fact if the meeting is taking a turn for the worse, you could say something like "I'm not currently assigned to project X, " and leave it at that.
A question you just don't know the answer to.
There are lots of questions that you can't be prepared for, or can't anticipate. If your don't know the answer, and it's not primary to your situation. Then a simple "I'll have to look into that" is perfectly fine, and in fact preferred.
What's the difference between the first type and the third? Your area of responsibility and the meetings purpose. If the meeting is to assess status of a project, then it's not ok not to know the status of your part. It is ok not to know total length of phone line that will be used during the next phase of the project.
For these meetings your the project lead for your part of project X, a project to build a giant letter X on the side of the building.
Q: When will you be ready to start painting?
A: We are still waiting on color choices, after that we will need about a week
Q: When will the color choices be in?
A: Bill is heading the task force in charge of color choices, I can ask him if you like.
Q: How much rope are you gonna need when you finally are allowed to paint the X?
A: I will have to get back to you on that, I don't have the figures in front of me.
The first question you really should know. It's a major part of your job. The second question isn't really your job, but you know who's it is. The third is a question you just could not have anticipated. It's still your area, but how were you supposed to know that it was gonna come up in a status meeting.
As a rule of thumb try to never say "I don't know" always "I'll have to research that". The primary difference is that "I don't know" is final. "I'll need to research that" is open ended.