how can download facebook old version to my iphone 3g

hi..

im using iphone 3g version 4.2.1 ..

but m not happy with this.

bcoz the common facebook app, true caller app all common apps not working on dis.

i try to dis itunes. but dis showing all time ...... required ios 5 ya 4.3

now i wht to do..

please help me.. bcoz without dis app .. i cant use this phone.