That way lies the path of not having a smartphone. All smartphones on the market involve some level of closed source - whether that's the baseband, the graphic

That way lies the path of not having a smartphone. All smartphones on the market involve some level of closed source - whether that's the baseband, the graphics blob, the chipset, the ROM, the firmware, or the complete operating system. Any of these could theoretically intercept the voice from the microphone / speaker, encode it and ship it on some back channel to the Five Eyes. At that point it's simply a matter of where you draw the line between paranoia (that the NSA are reading your thoughts and have compromised everything) / idealism (e.g. RMS) and ease of use.