Adam- great usage of a feature expressed only as an "auto-corrector." Quite clever. I like it. 🙂
Taz- You may not find the phrase "commonly used" anywhere in the Auto-correction.... just make sure you check off the box that says "Symbol and text substitution." Then click the plus at the bottom left and go nuts!
Alongside the above-mentioned method, there's a program that you can buy called
TextExpander that will also do the job quite universally across many applications. It's about $30. I have found it VERY worth the cost, personally. This isn't an Apple product, however, and not something built into Pages, so may not be what you're looking for.