Hopefully the open source phones catch up, because right now carrying around a general purpose computing device you have no control over thanks to the carriers strikes me as an astoundingly bad idea.
Having a phone whose OS is either compromised or deliberately acting against you is obviously unhelpful; but unless you control the baseband you are pretty much fucked regardless of the OS. Cell networks are fundamentally pretty hostile in terms of how much control is held by the network or at very low levels in the baseband, rather than where you can actually see it.
Sometimes you just have to hope for the best.
I like having a smart phone (and Android tablet), I was able to root the tablet before it became illegal. The phone calls out from the tablet (cyanogenmod ROM) that has Droid Firewall and permissions denied; the tablet through a router firewall. So no cell towers (if that helps much).
Hiding from NSA is or was never a goal, but from advertisers, while having everything at my disposal all the time, calendar, games, videos, and mostly the camera. I go to a parts store anymore, hold up my camera and say I need this
While a smart phone isn't necessary for it, it's just nice to be able to call anybody at any time, still remember scouting for phone booths at times with little luck.
Sometimes the best isn't always a goal, two things I still won't do with my cell phone (tablet) is transfer money from an open account (money cards ok) or use them for my Email. Email is more prevention (malware) than eves dropping. I expect my Email to arrive as text, reading it in HTML being my decision; still using Forté Agent 1.93 just for that reason (Windows).
Trust is also missing from a mobile device in a way that just occurred to me, Cell phone or tablet, I don't have one website I'm able to auto log-on to. Fact, I rarely if ever log onto a web site mobility, ya, the camera I carry it for the camera - changed stroke mid pool (Grin)
if avoiding NSA were my goal, it's been referenced already as the "Eye of Sauron"