This article was produced during Gadget Hacks' special coverage on texting, instant messaging, calling, and audio/video chatting with your smartphone. Also, sounds that show up can depend on your wireless provider, so you may see extra tones that are specific to the carrier in addition to the default ones or custom alert tones you've added. However, you can add them or any other sound file you want to your list of notification sounds with a file manager. Note that ringtones on your device will not show up as options for sounds unless they are also notification sounds.
