If you forget your sim number and worried about it! I'll say you should not :-) Here are few simplest steps for every SIM in Pakistan Telenor, Mobilink, Ufone, Warid and Zong.
FOR TELENOR: Send an empty message to 7421
FOR MOBILINK: Dial *99#
FOR UFONE: Dial *780*3#
FOR WARID: Write MYNO and send it to 321
FOR ZONG: Dial *100# and then press 1
FOR TELENOR: Send an empty message to 7421
FOR MOBILINK: Dial *99#
FOR UFONE: Dial *780*3#
FOR WARID: Write MYNO and send it to 321
FOR ZONG: Dial *100# and then press 1