this is a great application for N900
may i suggest a few things and i would love to have a reply on that pls.

if we could notice that if we block some number,how do we know if there was a call made from that number? there could be a notification or something like that only when you receive a call ( notification ) from a blocked number,so that you could count how many times that person called ya? ( notification again ) ;p ;p
can there be an option included for the whole country numbers to block? i am angry with my GF and she is in canada ,so i just want to block all calls from canada,how do i do that ?
could we have set another command other than that ( the person you are calling is busy at the moment ) ? as it could be ( the number you trying to reach is not available ) ( the phone is powered off ) ( number is out of service ) etc ?