There's an iOS app called GoSatWatch which will notify you when the ISS (or any satellite) passes by your location. Your location can be configured manually or by GPS, so you get the benefit of receiving relevant notifications when away from home. Apps like GoSatWatch will also tell you where in the sky the ISS will be, so you know where to look.

SpaceWeather has been doing text notifications for a long time (http://spaceweathertext.com/), albeit at a monthly cost. They've been doing it for a few years, I think. I'm not positive, because I haven't used their text service.