I would love to see VoIP. When you're in the middle of an assault or scrambling to put together a base defense, standing still for 10 seconds to type is a death sentence.
However, I've played on a few pug servers in which people were communicating well enough with chat to form actual strategies. So it does happen. What would be nice is if the quick bind messages were in a separate chat window, or a different color. It's easy for messages to get bumped off screen and disappear instantly when multiple players spam "Defend the power plant!", or for the message to simply be hard to read amongst a handful of spam because of the same color text.