FaceTime Audio is only restricted to WiFi for iPhone 4.
On iPhone 4s, 5, 5c and 5s you can use FaceTime audio via cellular. I do so every single day when calling my wife from work on my 4s while she's at home with her 4 connected to WiFi.
Thanks for the correction RebornProphet.
I remember trying it over one of the beta versions with another person who also had iOS 7 and the call didn't work for some reason. Back in the Beta days there was only 3 ppl I knew who had access to iOS 7 and could never get a chance to test drive this new feature with ppl. In general, I'm one of those who never talk on the phone, for the last six months I may have racked up on maybe 10 mins max of voice mins.
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There is one minor, but pretty major change I kinda miss when I traveled last summer, the complex password keyboard layout on iOS 7. During the summer I went on a trip to NYC, the land of the dash and grab for Apple devices. Being a tourist and all, it was the first time I've locked my iPhone up ever and adding the burned images in my head of corrupted city of NYC from 80s, everything was on high alert LOL
I normally have it off back home in Toronto, b/c jumping on a comp or the GF's iPhone is pretty instantly if I need to lock it up through iCloud for any reason of being stolen out of my hands. It's a rare thing to happen over here and ppl feel safer at home. In general it's such a pain in the ass to slide to unlock or slide my notifications to reply to whatever with a 4 digit easy passcode. It's so easy to peak at your passcode, since you gotta stretch one thumb across the screen and type it slowly. I found out with complex passwords on iOS 7, it was much faster and easier to execute, you just gotta find a word you know can type perfectly without any mistakes. Since you're in position for typing, this made little feature pretty useful and it's much better since you're typing a word very fast, ppl won't know what you're typing.
Scenario
1) Power up the screen by the sleep / wake or home buttons or it's already on when iMessage Notification arrives or reminding me
2) Slide to unlock the same area I would slide to unlock a iMessage notification for faster replies
3) Position two hands for a full keyboard layout, type in my complex password
4) Already in position to type a reply, wait for the animations to complete and fire away & send.
Oddly in iOS 6 the "setup" of the complex password keyboard layout is just like iOS 7, but in the real lockscreen the return / OK button is right next to password entering field box and I gotta reopistion my thumb to hit it & return back to the typing position. A very minor adjustment, but it shouldn't be that way. The return button which should be at the normal area is the emergency call button, talk about crazy thinking here.
In a way Touch ID is kinda useless for me, 80% of the time I'm sliding to unlock a notification I want to replay to and I still gotta type out a complex password to unlock it.