I've tried services likes this before but it's too easy to know what it is and ignore it and then fall back asleep. Maybe I'm just more stubborn than everyone else.
Have you ever tried something that tells you what to do? I've tried things that wakes me up with music or all kinds of things, but the key here I think is the message you can write to yourself. If you could tell yourself all the things you need to do for the day, that would be a really good way to start the day. Because I find that even when I do wake up most of the times I just do nothing productive. I think it's great to hear a todo list when waking up.
There's still the issue that you have to answer your phone with this service (provided you don't write an Android app that automatically answers calls from this number and puts them on the loudspeaker). Once I get used to knowing the phone call will happen every day, I'll just start holding the pillow around my head until the ringing stops and return to sleep.
I'm much more tempted to write something for a Raspberry Pi with speakers attached that will immediately begin yelling at me at the proper time. More configurable, and less prone to weird phone-related issues. (The only vulnerability would be if I started unplugging the device or speakers in my sleep, but there are ways to mitigate that.)