>   Is there a standard or preferred pin assignment when a RJ-11 > connector is
> used for a RS-232 connection? Also, how are the pins numbered?

Yes. There are many standards to choose from ;-)

Look at:

http://www.hut.fi/~then/mytexts/rs_rj45.html
http://www.advanix.com/~neuhaus/serial/index.html
http://www.yost.com/Computers/RJ45-serial/
http://www.cisco.com/warp/public/701/14.html

Actually those are mainly for RJ-45 but some have a (can be) scaled down
version for RJ-11.

Good luck!

Ciao
  Marco