Well, the question isn't so much whether you need a smart phone or whether you want one.
Lately, I've been using mine for multiple purposes that required me to carry other stuff:
1. maps (including a star-mapping program) and trail descriptions
4. a movie or two and a few Monk episodes for those nights I can't sleep
5. oh, yes, as a phone
The big problem is recharging. Mine is in a battery recharge case, and that extends the life of the battery by about 2x.
The think is, I don't really need any of the things above, except maybe the maps (and I tend to minimize their weight when I carry them separately anyway), but they do make the trip considerably more pleasurable, especially on those long, lonely nights when sleep will not come. The fact is, if you hike in the wild where nobody provides phone service, you probably won't use the phone anyway. Sometimes, I'll call home to check in as I'm losing phone service, and then hide the phone in my car, and leave it there. The minimalist in me doesn't want the phone, and I go out to escape the issues that the phone reminds me of. The thing seems like a burden most of the time.