iPhone5 - or Android smartphone
cheaper than PSV and it has more functionality, as in, you can use it to call people.
Since you already need to carry a phone around with you everywhere, no need to have two different handheld devices. The PS Vita would be extra dead weight.
If you're playing demanding games on your smart phone, you probably won't have enough battery life to make those needed phone calls

Sorry, but I also can't help but laugh at you saying an android phone or iphone is cheaper than the PSV, because that's not the case. If you get it subsidized then you are locked into a contract and must pay the necessary fees as such, if you get it out of a contract they are certainly more expensive than a PSV. The PSV has no such necessary contracts.
Also, a smart phone does not have more functionality than the PSV, just different functionalities.
Edit: in the end, the OP's choice is a non-choice considering the iPhone 5 isn't just around the corner and hasn't even been announced.