My chapter used both: email for long things, instructions, and important messages, but mass text for timely reminders and annoucements that were less serious. I get 31838475 emails a day and loved getting texts instead; ain't nobody got time for "hey ladies, don't forget the panhel speaker starts at 3 today!" clogging up their inbox. If I'm busy and I get a sorority email I'll probably ignore it til later, but I'll read a text.
And we use the GIN system and GroupMe
GroupMe gets tricky with adding more than a certain number of people, but it's awesome for quick and dirty mass texting.