Why no "situational awareness" (collision avoidance) apps for cell phones?

Smart phones can talk to each other (through the cell system, duh) and they have substantial computing power. They have GPS so they know where they are, how high they are, and how fast they are going. We know they can output and receive that data in flight because we use them to track our gliders giving out our position, climb rate, and ground speed and we can view those tracks on the very same phone. I would guess that there's a smart phone in the cockpit of nearly every light aircraft flying. So, my question is: Why is there no situational awareness app for our phones? Yes, I know about the limitations of the cell system and the phones, especially in flight. I wouldn't expect a cell phone based system to perform in every category as well as the all singing, all dancing PowerFlarm. In it's favor, such an app could be nearly free compared to $2000 for a PowerFlarm setup. Considering the "installed base" of smart phones, the penetration of such an app could be very rapid and widespread, maybe even approaching near universal adoption. So what if it does not do everything that a PowerFlarm does? Even if it only provided a snapshot of the local traffic every 5 or even 10 second, the safety benefits (outside of racing gaggles) would far exceed PowerFlarm simply because of the potential for such rapid and widespread adoption. Everyone could finally see everyone.

C'mon, I know I ain't the first person, or even the 10,000th to have this idea. If I had any idea how to code an app, or the time to learn how. I'd give it a try myself.

WB (doped to the gills on cold meds and exhausted from a 950 mile drive, so forgive me if the above is gibberish)