Is it possible to turn Android device into device that is a Software Defined Radio (SDR)?

Software Defined Radio (SDR) devices are very costly and not everybody can afford them. Even if they could, **some people are not willing to invest their one-month salary into it.** There are RTL-SDR dongles in the market costing some ten dollars, but this is not about external SDR devices. I am thinking of making some code changes in the Android Linux kernel to act as the wireless-cellular chip as SDR. There are projects in XDA Forums where they have built codes that put their WiFi into monitor mode, let's say it is a monitor mode support driver for Android. So as a context to that; what I am trying to do is; make/write some code changes to the Android Linux kernel which will set the cellular chip into SDR mode. Is it possible? If it's possible, then can you give me some ideas on where to begin? I expect only Android core developers from the networking field to correctly answer this question + those of Android hardware engineers.