Go for an Android device. It has the best support for Bitcoin as of today.
With the iPhone and Windows phone you never know if an what kind of Bitcoin apps you'll get and they could get taken of the appstore any moment.
There is no app on iWhatever that allows you to send Bitcoins. Apple just does not allow it.
See e.g. here:
http://www.coindesk.com/apple-approves-bitwallet-ios-app-btc-sending-function-blocked/-snip-
I recently purchased some coin, took a picture of the receipt and tried to attach to email but couldn't.
-snip-
Please dont do that again. Sending the code that allows you to get the coins via EMail is a very dump idea. Sniffing mails is way to easy.
As state above iPhone has no App for Bitoin. Apple does not approve
Android has several you can choose from but AFAIK all of them had problems in the past. Mainly because its a phone and thus not very secure. Im not talking about stealing it, but rather about the limitations of the hardware. Andoird had problems with its random number generator.
If you must use a phone do not load more bitcoins on it as you would carry around in cash. Keep the rest of your coins safe at home.