*# Starhash Enabler finally turns your N900 into a full-featured phone capable to dial Service Codes like *67# call redirect on busy, etc.

Some useful codes: **61*# : set up redirect to after ringing #61# :deactivate; 61# :activate; *#61# :query status replace 61 by: 21:all calls; *21*#; *21#; #21#; *#21# 62:if off or in a cave; 67:when busy (other call); 004: eq: 61+62+67; 002: eq 004+21

Google for gsmcodes to find many more. Please note the Settings-Phone GUI won't know how to deal with network settings done via this method! Also note it's up to your provider to actually support or lock particular functions/codes. Frequently has to be the number of your voicebox.

Credit goes to Lassi Syrjälä (Nokia) for https://bugs.maemo.org/show_bug.cgi?id=5357#c178 MohammadAG for doing all the packaging setup and helping

Now comes with approval by Nokia :-) https://bugs.maemo.org/show_bug.cgi?id=8830#c18