Finally. Tuomas Eerola has released the series 60 version of the great app that has been only available for 92xx series phones previously. It answers incoming calls automatically with predefined SMS messages.

From Author:

SMS ASSISTANT FOR SERIES 60 V0.09

Frustrated because of not being able to answer your incoming calls or messages? SMS Assistant is the solution. SMS Assistant for Series 60 is an "out of office assistant" for Series 60-based smartphones. SMS Assistant sends your predefined message automatically to people calling you or sending messages to you. You can concentrate on your work or favourite hobby without having to think about people trying to reach you.

Get it from here:
http://www.cs.tut.fi/~eerola/tuomas/download.html

Price: Free!
Version: 0.09
Size on phone: 30kB