Can an android phone be converted to SDR using its radio hardware interfaces?

I have recently been reading about SDRs and based on what I have understood so far SDR consists of a radio hardware capable of transmitting and/or receiving radio signals within a given radio spectrum range and a software backbone to control its radio operations, so I thought it should be possible to achieve similar operations using an android smartphone therefore I tried to search for projects in the internet and the closest I have found is SDR Touch which requires an external dedicated hardware. Now since a smartphone has so many radio interfaces (Cellular, Wi-Fi, Bluetooth, GPS etc.) is it somehow possible that I can make a project (using root or whatever) that utilizes smartphone's radio components and why isn't there any project that exists performing such functionalities?.