dialing phone number manually using keypad which prevent me from editable

I am not able to edit the dialed pasted phone no on my keypad. I sometimes receive phone numbers with an SMS or mails, usually with a missing prefix. For example I ask a friend to send some contacts. He sends it say, as 96666 55555. All I want is to copy this number, paste it to phone keypad screen, change it to 096666 55555 and call the number. I don't want to add it to contacts or paste in notepad. I just want to make a call and I am done with that phone number. So far it is impossible to edit a number which is pasted on the keypad screen. Is there really no way of managing this? I have Iphone4s and on latest iOS firmware.