There is nothing that can shorten the lifespan of a book (or movie) quicker than references that make it seem dated. But how do you write for today's teens without including the ever-evolving latest technology that is so much a part of their lives? If you want your voice to ring true, you must. However, you need to keep on top of what the latest trends are.
For example, when I was a teenager, it was a big deal to get one's own phone line, and to communicate with my friends, we hung on the phone until all hours every night and wrote notes that we slipped in each others' lockers in the mornings. (And no, I did not also ride a dinosaur to school.) However, when my sixteen year old son wants to communicate with friends, the phone isn't even on the short list of possibilities. In fact, the mere suggestion of actually calling someone and speaking to them incites strange looks and rolled eyes, as if that is just simply too much effort. Even email, according to him, is already old and outdated by the time one gets it, reads it and responds. Kids today want everything instantaneous. Therefore, they text. Incessantly. They instant message. Sometimes they Skype. Sometimes they group chat online or on Facebook. But they rarely talk on the phone.
Chances are, whatever scene you write today about the mode of teen communication, or the game system they are playing on, etc. will already be somewhat outdated by the time your book goes to print, so sometimes it's best to keep things more general. For example, cell phones will be around for awhile, but the style or the features will rapidly change. Your characters may be playing Halo 3 on their Xboxes, but by the time your book comes out, they may be on to Halo 6, or Halo will be a game no one plays anymore, having been usurped by another hot title. Try and avoid referencing specifics unless you are writing something along the lines of THE FUTURE OF US by Jay Asher and Carolyn Mackler, in which the character exist in the 80's and are accessing their future selves. And what makes THE FUTURE OF US so damn funny? Among other things, the references to things like the AOL start-up discs we all got in the mail offering 100 free hours. Instantly, we're transported to a different time. If your book is set in present day, you want to make sure your readers really do feel like they are there.
If you're in doubt as to what the latest technology and trends are, I can't recommend enough the starting point of sitting down and talking to a teenager. They'll tell you everything you need to know. You can also regularly peruse websites like cnet.com, which talk about new technology, and keep up to date with the latest unveilings from Apple, etc. Keeping yourself savvy will lend authenticity to what you write. And obviously, if you're writing something in the future, use your imagination, building upon the realities of what exists today so that it still feels like something believable.