Do you write the way you speak? Do you speak the way you write? Probably not. Although talking and writing are forms of communication, they're often very different. Writing is, in general, a more formal pursuit than speaking. When writing, we tend to take our time, add punctuation, re-read sentences, and think about our words. When speaking, we tend to rush forward without looking back, spend less time on word choice and sentence structure. Think about it this way: if you're debating someone in an email, you're likely to construct carefully crafted sentences that define and elaborate on your points; if you're debating in person, you're likely to quickly and passionately defend your cause.
The way we write is just plain different than the way we speak, and that's okay - for the reasons I outlined above, it's supposed to be.
But what about when you're writing something that's supposed to be spoken? Like a script? For your company's Message on Hold program?
That's where things get a little tricky. For the most part, a script that is going to be read by a professional voice over talent is going to be written with a more formality than colloquial use. If you're featuring content on your company's phone system, it's understandable to want it to sound professional, planned, and proper. But at the same time, it's going to be read out loud, and it needs to be listenable, so slipping in some colloquialisms and contractions can actually be useful.
Interestingly, people frequently use contractions and don't realize it. They're a normal part of our speech and thinking. Overusing them is annoying, but so is underusing them.
Here is an example. I am currently writing these sentences without using any contractions. Even while I am reading in my head, I cannot control the robotic-sounding voice.
But if I were to rewrite those statements with some contractions, it would have a more readable flow:
Here's an example. I am currently writing these sentences while using contractions. Even while I'm reading this in my head, it's a major improvement from the previous, full-worded version.
As you can see, it's all about balance. While writing has some universally accepted formal rules, speech is much more fluid, frequently changing, and relaxed. So even if you're writing and script, remember that it is ultimately going to be spoken - and don't be afraid to loosen up a little bit.