The biggest thing right now for those ages is adding social media to the phones(facebook, twitter, etc.) If you do a search of new phones you will see that this is something that most new phones have. Bringing together everything that younger people do is huge, because people are looking for an easier way to do everything. If someone can have 1 device that allows them to do just about everything then they are more likely to buy it.
Also having e-mail, camera/camcorder, and applications that can cater to anyone is huge(app store like the iphone and droids)
Hope this helps!