If you're integrating with a phone, you'll need to decide if you want this to be something you can access locally or from anywhere.
If from anywhere, you'll need to create a login of some sort. You'll likely end up using web services to do that piece. If you're only worried about locally, you can find a variety of ways to handle this such as data dashboard.
Simulating sensors is the easy part. You know what values they can have. You create a control. You put values in the control. Now, you have a simulated sensor. When you get the actual sensor, you replace this control with the logic to read from the sensor.
