In a few days, you'll be able to talk to your iPhone and iPad by saying "Hey Siri..." http://www.idownloadblog.com/2014/06/02/ios-8-siri-changes/
Apple is trying to compete with the "OK Google" phrase that you can use with Google app and website.
But I already talk to my phone, and I start every conversation with "Hey Emily, would you…"
I played around with the words I use (the "wake up phrase") because nothing felt natural, particularly in public. But now that I have a phrase that feels right to me, I use my voice activated assistant service much more frequently and easily.
While I don't think Apple will let you customize their built-in wake up phrase "Hey Siri" other apps WILL let you do it. I highly recommend customizing if you can.
My favorite app is the Dragon assistant app for Android (I also use an iPad). I tried wake up phrases such as "Hey Dragon, do this…" for awhile, and before that briefly toyed with phrases such as
• "Okay assistant…"
• "Open up and…"
• "Do this for me…"
Once I found what I liked, I went even further and created contacts called "This task for me," and "This task for shopping," etc. and so now I can say things like
"Hey Emily, would you email this task for me, Subject…" and it makes being productive just feel a lot more natural. (My tasks appear automatically on my to-do list in Asana using their email a task technique.)
(And how did I pick the name "Emily?" I asked my wife Sarah to suggest a name she wouldn't mind hearing me say :-)