Keep on waiting, it's likely never going to happen anytime soon.
It was only used for the sim tool.
Actually, if you all recall, Apple bought Liquidmetal AFTER they tried it out with the sim tool! I've seen a post where they're supposedly going to use it for some new battery technology, but I think that may be a distraction...
iPhone 5 in liquidmetal would be the best!

...but aluminum is definitely a possibility if they can work out the antennae issue...AND to the naysayers that say Apple won't go backward:
1) pretty much every Apple product is made w/ aluminum
2) won't go back to an old design?? Then why does the iPad 2 look more like the iPod touch or original iPhone, and less like the first iPad?
3) Customer service ratings:
There are several problems with the iPhone 4 design to consider:
a) Glass backs break too easy resulting in:
Apple loses $ to replace OR higher rate of customer complaints (also, they don't want to make a pretty design that has to be hidden in a case... i.e.: the iPad2 & "cover" designed together)
b) ...still haven't worked out issues with making a white version
c) Apple won't settle for anything less than a Consumer Reports "Recommended" rating. ...whether you agree w/ CR or not too many Americans listen to them for Apple to ignore this.
d) a, b, and c are all negatives that Apple will not allow to degrade their customer service ratings. ...if you go by the OS numbers, android OS is gaining ground and Apple will do whatever it takes to keep iOS on top!
This mockup
could be Apple's design direction for the rumored less expensive iPhone, or perhaps both (and yes, looks like iPod touch, iPhone 1, iPad 2 ...and those all have similar curved edges as the MacBook Pro unibody covers). For me personally, I really hope the next iPhone has a liquidmetal or aluminum back, if it does, i won't have to get a case for it!