R++ is a "Smart" application which allows you to reject incoming calls (while you're busy) with predefined or custom SMS as well as set up a smart reminder to return the call back.

Reject++ Main Feature:
#1. Reject a call by SMS only, Reminder only, or Both.
#2. SMS Templates with descriptive "Tags" & lengthy "Text", unlimited and fully configurable.
#3. Reject with Smart Reminder Features:
- Different Scheduling Options to use like
... Fixed Duration: Every 2 Hours (configurable)
... Free Slots: Tell the scheduling engine about 3 slots you are usually free during the day (i.e. lunch break, after work, before bed time, etc) and the scheduling engine will schedule your reminders to these slots on first available bases.
... Last Reminder: you schedule the first, and the rest follow.
... Custom Time.
- Scheduling operates manually & automatically
#4. Status Bar Notifications: when your mob screen is off or locked, you will still get it
Much More: http://gxeed.com/Reject-Plus-Plus

Screenshots: