How does the antenna design on the iPhone 6 work?

I did not closely look at the iPhone 6, which has aluminum upper and lower parts. Was basing my answer on iPhone 5/5S design, for which here's for example a quote:

"As industrial designer Don Lehman has explained, the iPhone 5’s back panel features a cell antenna on the top and bottom of the device, surrounded by a thin strip of glass that allows Wi-Fi, GPS, Bluetooth and other signals to “peek” through. These antennas are so far apart that unless you have freaklish long hands, it’s impossible to “bridge” them with your grip. So long Antennagate."

(Read more here).

What happened with iPhone 6? The metal parts became the antennas?

Metal bands are always antennas. Look at iPhone 5/5s, the GPS/cell secondary RF connection is just a stub, the band structure it connects to is the main deal.

I have no particular knowledge in antenna design, but the way i understood it is that every antenna has to be a specific length to emmit a certain wavelength of radiation/signal. in order to make the antennas smaller it is also possible to use a fraction of the needed length as in 1/2 1/4 1/8 etc. and tuning the signal that goes through it to "emulate" the right wavelength by resonance. my guess would be that the engineers have figured out a way to use the metal bands as antennas for multiple purposes (wifi+cell i.e.) by tuning the signal that goes onto the metal band so that it emmits signals in 800mhz and 2,4ghz simultaniously. but then the question is, if the "radio" adapts to the antenna (metal bands) hooked up to it, you could theoretically hook that radio up to any kind of metal thing and it would still work (more or less efficiently probably, but still work, as long as its isolated) ?

@Romazzino, the length of the antenna as you said, and the ensuing wavelength that is emitted are what caused the "antenna gate" for the iPhone 4. I'm not sure if you knew about it. So to make a long story short, sometimes people held the phone in a way that bridged 2 insulated components (the antenna with the rest of the frame), rendering the antenna longer and consequently the wavelength different. That caused the iPhone 4 to drop calls. Apple solved it by offering free bumpers that completely insulated the whole frame and prevented the accidental bridging. Then they resorted to a different design with the iPhone 4S and beyond.

@Rany, the design in the 4S is essentially no different to the design of the 4. Only difference was the addition of one more antenna that the phone can alternate between. But its basically the same design.