Well, you register for an account, and you get issued a textPlus number, which people without textPlus can use to text you (free) or call you, if you buy minutes from textPlus.
textPlus users can use either your number or your username. For simplicity's sake, we'd like to try using our CP usernames, or a "PS3<Team>" format, if you're creating an account solely for our league. Like, I created a personal account, and then I created one with the username "PS3LAKINGS".
We've got a thread on the new forums where people can post their textPlus usernames, and I add them to the master list in the first post of that thread. I'd also recommend throwing it in your forum signature as well.
So far we've got 7 textPlus usernames on that list.
http://cpconnected.x10.mx/viewtopic.php?f=5&t=48