OK, I found a solution for my call forwarding problem with my Nokia N900

First, I am from Canada and I am using phone service with this company: http://www.fido.ca/

The condition may be different if you are from a different country or you are using a different company.

To call forward your call:
1.Open X Terminal
2.type «pnatd»
3.To call forward to number 14186562131 type «AT+CCFC=0,1,"+14186562131"»
4.To cancel call forward type «AT+CCFC=0,0»
5.To check if the unconditional call forwarding is on or off type «AT+CCFC=0,2»

According to my phone company, *21*14186562131# is the USSD code to call forward. (http://www.fido.ca/web/content/faq/faq_call_forwarding)

This doesn't work with my nokia. I tried ussd-pad and ussd-widget without any success

To found the solution, I used those two links:
http://sw.nokia.com/id/95672052-6c77...ts_v1_2_en.pdf

http://www.forum.nokia.com/piazza/wi...T-Commands.doc

Thank you everyone.