Smart Watches - Ironman

I assume that many people wear Smart Watches in WTC events? Just wanted to check before I show up with one. I'm only planning on using it for GPS / etc. The Athlete Guide says:

we can't use them in a “distractive manner”—in their words, “making and receiving phone calls, sending and receiving text messages, playing music, using social media, taking photographs and mounting the device to a bike for purposes of using the device like a bike computer.”