One of those options is that the film cuts away at that point, and we (the audience) don't get to hear what the plan is as the character explains it to whoever he was talking to. Then, as the plan goes into action and it unfolds, we are surprised at how it twists and turns as the characters execute their plan.
Here's the scene from the first "Pirates of the Caribbean" where Jack steals the Interceptor out from under the British Navy that illustrates this first approach.
Jack never says "I've got a plan" per se, but it's pretty clear he has one and at no point do we (the audience) know what he's up to (nor does Will Turner, it seems). So as the plan unfolds, everything is a surprise to us and fun to watch...all the way to the end, where he anticipates every move his enemy will make to try and stop him. If we had heard all those details in advance, it would take all the fun out of watching it unfold.
The other way to go is that after the character says, "I've got a plan...", we do the opposite: we don't cut away. We stay with the character as he or she lays out their plan in detail. That way the plan - as the characters are expecting it to unfold - is clear in our minds. We know exactly what each character's role is in the plan, what they're supposed to do, and when, and what the characters expect to happen at each point and what they expect the final result to be.
The reason to play it this second way is so that they audience is completely clear on what's supposed to happen....and then dramatic tension (or comedy - think "I Love Lucy") is created when the plan starts to go completely wrong. Maybe the world doesn't react the way the characters thought, maybe the guards decided to change their schedule that day, maybe one of the characters falls asleep and misses the crucial step everyone was relying on him or her to perform. Doesn't matter....the point of this second way is to set up an expectation and then create drama (or comedy) by how the plan doesn't match what we were setup to expect.
The point of both ways is to surprise you - either by completely withholding information or by giving you all the information you need so that you can understand what's going wrong and how bad that is for the characters.
Think how boring it would be to hear the characters plan out their moves and then see them execute it in exactly the way they planned it out. It'd be like watching the same thing twice....once as they talked through it and then as they actually did it. It's be like watching a movie where everyone says what they're going to do before they do it: "I'm going to punch you now", "I'm going to shoot you now", "I'm going to kiss you now".
In a lot of ways, this little example holds the key to much of film making. Either withhold key information to surprise your audience with later, or setup an expectation that you subvert later by delivering something else. It's that simple. As Jerry Bruckheimer once said about film making, "Just keep throwing 'em curveballs."
WARNING: POSSIBLE SPOILERS (but not really)
"Mission Impossible: Ghost Protocol" falls into the latter category: that is, they have a lot of plans in the film and they definitely explain them out in advance for the audience to hear. I don't think there's any other way they could have approached it in that particular case: the plans in the movie are so complicated there's no way to explain everything that's happening to the audience as it's happening. And their plans are so reliant on getting technology to work in unison with the physical parts of the plan that I don't know how you'd ever explain that while it's unfolding. It would make no sense and would create pauses in the action that would totally destroy the rhythm of the action sequences. So they discuss their plans with each other before they put them into action, and they explain the technology-based parts of their plan to the audience in a natural way: they have one tech-savvy guy who understands all this stuff better than anyone else on the team, and so the rest of the team naturally has to ask him questions about all the technology, and he explains it to them....and to us, the audience. So as we jump into the action, we know as much as we need to know to understand what's happening and what the technology is supposed to be doing (and what it's not supposed to do, so we know when it's failing). Otherwise there'd be no dramatic tension if it started to malfunction or do the wrong thing.
There are better examples of this type of thing in the film, but here are some clips that are available online that illustrate the point.