One of the most useful changes Apple made to the Phone app in iOS 6 is the ability to quickly reply to calls with an SMS or iMessage, as well as the ability to sett callback reminders so you don’t forget to return an important missed call.
Using these new features is quite simple. When a call comes in, notice that there is now a small phone icon next to the Slide to Answer button. Slide that phone icon upward, and you’ll be presented with two choices: Remind me Later, or Reply with Message.
Tapping one of these two choices will send the caller to voicemail automatically. If you select the Reply with Message option, you’ll find a list of quick messages to send, including “I’ll call you later,” “I’m on my way,” or “What’s up?” You can also enter a custom response, or set up long-term custom responses by entering Settings, tapping the Phone pane, then the Reply with Message pane, and entering three personal responses.
Choosing Remind me Later, on the other hand, allows you to set a timed or location-based reminder to make sure you don’t forget to call the person back.