The phone app only replays a recorded message from yourself. I have one that runs on a laptop that does text to speech (it plays my music getting gradually louder with the time spoken every minute along with any other messages you want read out (either every minute or at specific times)).

I didn't have much experience with text to speech before this so I just used the open source stuff I knew about (espeak and the mbrola voices). I want to find a good way to do this in the app because I like the functionality so much that I use the laptop app more than the phone app. I'm talking about android so there are a few options I'll look at when I get back to this project.

I can see doing it as a service if you plan to add all sorts of magic on the back end (text to speech, read news/headlines/weather to you). All stuff you could do in an app but when you have that many features you can charge a monthly fee instead of a one time app sale and you can probably monetize the user data as well somehow. So yes, it does make sense.

For some reason this kind of thing trips my privacy alarm, I would be uncomfortable sharing the messages with a third party (even if the most personal message would be something like "get your lazy ass up on time today, you haven't gone for a run in three days"). On reflection this is probably just me and wouldn't apply to most people, I have a strong bias against storing private data or messages in the cloud because I work in those industries and am aware of how common it is to trawl the user data for funny stuff to share with coworkers.

More than likely using the Twilio Text-To-Speech API: http://www.twilio.com/docs/api/twiml/say