The new larger phones are expected to sell out by the end of opening weekend as Apple scrambles to get more inventory into stores.
"This will be the biggest iPhone launch since the introduction of the first iPhone," said Tim Bajarin, an analyst with Creative Strategies.
Aubrey Nelson, 35, says she plans to pre-order the iPhone 6. She already sold her iPhone 4s on Gazelle for $105.
"I'm perplexed by the move to wait in line for days or hours for a phone that can be pre-ordered online. It's a bit ironic that those craving the latest tech don't take advantage of it when buying the tech itself," said Nelson of Burbank, Calif., who works in human resources.
'Coveted new toy'
"I'll be up late tonight, albeit in the comfort of my bed, watching and waiting for that midnight drop," she said. "My credit card information stored in my trusty MacBook for expedited ordering. Coffee on my nightstand lest I succumb to the sandman's subtle attempts to sabotage my goal of attaining my coveted new toy."
Gene Munster, an analyst with Piper Jaffray, says people like Nelson will help Apple sell 92 million new iPhones by the end of the year. There are currently 300 million iPhones in use worldwide.
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Jamie Dunham, a 63-year-old brand strategist from Nashville, Tenn., says she's staying up until 2 a.m. CT so she can pre-order the iPhone 6.
She says she has been waiting since last October when her AT&T contract was up for renewal.
"I am a bit desperate. I have a 4s and it's on its last legs. I have been holding out on my contract to get the new iPhone 6," she said.