Jailbreak is a method for giving your device the ability to use such an awesome tweak. without it call recording is not possible. Look at the 'How To Install' page on this site on how to jailbreak your device.

4. Does iOS Call Recorder requires any external service or making a conference call ?

No. The beuty of iOS Call Recorder is that it does all the recording straight on your device without using any external service (like calling a spammy call service which does the recording for you). All recordings are saved on the device natively and quickly. no hidden costs. it's a one of a kind tweak for iOS which no one has done before.