Calling a phone with dead battery

[pearldrumbum]

Either i suck at using the search function... or no one has asked this, which i find hard to believe. But for you iphone experts it should be an easy question.
Girlfriend claims phone was off but it rang all the way through to voicemail. She has iPhone 4 (not S) with at&t. I did a test with my buddies phone and it went straight to VM when off, but he has verizon, so not sure if that makes a difference. I did a google search too but it only brings up those dumb quick answer sights where no one cites their sources and no one agrees. I figured this should actually be a fairly simple question to answer....
Thanks (i know its petty, and not really a tech question, but any knowledge you cam share is much appreciated )

Edit... guess i never asked in the form of a real question. Can her phome ring all the way through when its off due to dead battery? I was under the impression all cell phones go straight to voicemail if not turned on...

 

[Mr.Mischief]

If a phone is powered off, and you attempt to call it, it should go directly to voicemail.

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[ZanderF]

once the phone is off there is no chance to phone at all maybe 911 but I don't know excatly