For the killstreaks, you have to level up to about 67 to unlock them all.
For the callsigns, you need to complete every challenges in the game.
No, call signs were not introduced until Modern Warfare 2.
By completing challenges.
well call of duty and modern warfare are the same it is called Call of Duty: Modern warfare and then came call of duty: modern warfare 2
yup
Call of Duty 4: Modern Warfare came out first. This is the first game in the Modern Warfare series, and Modern Warfare 3 is the third game in the Modern Warfare series.
http://callofduty.wikia.com/wiki/Callsigns
Call of Duty Modern Warfare came before Call of Duty Modern Warfare 2
no theres a call of duty modern of warefare 2
"Call of Duty 6" "MW2" "Modern Warfare"
"Call of Duty 6" "MW2" "Modern Warfare"
Call of Duty 4: Modern Warfare was just before Call of Duty: World At War, and Modern Warfare 2 came just after it. Unless its on the Wii, on the Wii its WaW the Modern Warfare but its called Modern Warfare Reflex
You can get them many ways such as leveling up, completing challenges, etc.