Why do so many characters use iPhones in TV shows and movies?

Obviously Apple pays for product placement, but think about it this way too, think about the people who make the shows... they probably want their characters to appear affluent, fashionable, modern and part of modern culture - what choice of companies and their products give that vibe by association (a kind of shorthand) without having to explain it through dialogue?  You can show areally  nice looking ACME 'All-in-One' (with all the latest features) and just hope your audience is savvy enough about the the latest technology brands to clearly understand how affluent/modern/creative the character using the ACME 700HX is or you can throw them in front of an iMac and be pretty damn sure your character is getting clearly defined. Also, think about aesthetics. Every inch of a TV show's set is deliberated over, it is a visual medium after all.  The style choices made by the production team for practically everything you see on-screen from the clothes the actors wear, to the actors themselves, to the colours of the furnishings are thought about well in advance.  A PC on a desk that looks like an unbranded dark-grey or black box is not necessarily a clear decision and just takes up space.  So what brands would come to mind when thinking about putting good looking computer hardware in your frame?  Apple isn't the only one making nice hardware (finally!) but which choices really make the most sense to put on screen?  The thin, quiet one with the nice aluminium curves, single cable and no buttons that appears in competing TV shows on other channels or the slightly funky or modern-but-still-a-business-model with the cheaper looking mouse and keyboard?  Or maybe the one that looks like an Apple but isn't really?... And it's not just the visuals. When a phone rings on a show, and you want your character to pick it up and have that all important plot defining conversation what ringtone do you use?  The discreet common one that even non-iPhone owners have heard on the bus (and on other TV shows) or do you want to play a custom sample of 'Sex on Fire'...? Obviously you want to use an iconic sounding ringtone as a simple, unambiguous and clear audio cue for the audience (and not a pop track or one of dozens of other brand's ringtones).  Or to put it another way what is the go-to iconic Windows Phone or Android ringtone that you can play off-screen and get the audience to grok instantly?... Maybe we can understand why Apple might have thought that creating a decent and unique ringtone for the iPhone like Marimba was important... Brand building can be much more than just coming up with a cool name and sticking a logo on everything.  If you do it right your products can transcend sales and marketing and become part of our culture too. As a final point, I have noticed several shows (30 Rock, The Big Bang Theory, Happy Endings... ) which feature Apple hardware but often carefully cover the Apple logo with quirky stickers or hide them behind props.  Apple hardware being used on TV but not as direct product-placement?  It is almost enough to make you think that TV shows and movies are sometimes merely reflecting the real world back at us and they are not being paid off by Apple at every opportunity.

Mainly product placement. But, I have also heard of instances where film makers are huge fans of particular brands, Apple in this case. For example, IMF operatives in Mission Impossible: Ghost Protocol mainly use Apple products because J. J. Abrams is a supporter of the same.

For much the same reason that if you look back on slightly older shows and movies you will likely see people using Macs whenever a computer is involved. Apple does a fair amount of product placement, which has been very successful for them. This tactic is now used by Microsoft, Dell, and others to promote products. A few months ago Microsoft spent a lot of money to promote Windows Phone 8 and Skype on several TV shows. I am not sure of the origin of product placement, but Apple was definitely an early adopter for the modern computer industry.

But the recent seasons of Vampier Diaries,they all uses Samsung.

Its primarily brand advertising. In any show or movie if you can see a brand name then it is for advertising, if they do not want to advertise then they would cover the logos, as you can see in cooking shows.

Couple of reasons - most of the tv series like to see are from america - IPhone owns the American smart phone market - It's a brand statement for celebrity to have iPhone.. Obviously you do not expect famous people to carry economic goods you expect them to carry stuff Thats costly irrespective to their usability