Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
TextNow - TextNow is a mobile virtual network operator (MVNO) that provides a free phone service to users by using other cellular networks coverage.
BuildFire - BuildFire is the easiest way for small businesses to build a mobile app in a matter of minutes for iOS and Android.
Burner - Disposable phone numbers -- now with MMS photo support
MIT App Inventor - App Inventor is a cloud-based tool, which means you can create apps for phones or tablets right in your web browser.