I have used Google Voice with great success in both my flipped and traditional classrooms. Once you sign up Google Voice give you a phone number that students may use to text or call you without having to give out your actual cell phone number. It's a free service. You can download an app for your phone here. I require that my students notify me if they ever have a technology issue when I have assigned a video to be watched out of class.
Since I have started using the Remind 101 app available through iTunes and Schoology I have increased student viewing of videos from around 50% to around 90+%! Once you create your class name in Remind 101 it generates a pdf instruction sheet that directs students and/or parents to text or email a specific to a phone number or email address. Once they register they are automatically added to your class roster. You do NOT have collect phone numbers or email addresses. All of the responsibility is put on students. I typically have students get out their cell phones and register on the first day of class.