Is it possible to be productive with only a smartphone?

Try this : https://play.google.com/store/apps/details?id=com.aide.ui... -> You can develop android apps on android itself.

I know this is referring to programming, but I went overseas to study for two months this year with only my Galaxy Nexus, so this is my experience:

Yep, to a limited extent you CAN live with only a phone (and be quite productive!). Expect to use a physical notepad a lot too though, as flipping between apps even on Android 4.1 constantly is no fun when you need to keep referring to information.

Battery life is a KILLER. I get a whole day out of my Galaxy Nexus back home, but when using it exclusively as my only technology, it lasted me half a day max. 8am to 1pm if I'm lucky.