Question: Since many days I am trying to achieve this, but I can only delete/ clear all recent dial, received phone numbers.

Is there an option/ hack to delete only one number at a time on my iPhone ?

I have iPhone 3GS

Answer: 
If your iPhone is jailbroken you can install the package [Ixtension](http://ixtension.com/) (it's $9.99 from the BigBossRepo)

Disclaimer: I'm in now way affiliated with the developers.
I doubt iOS allows you to enumerate recent calls through standard iOS apps. I would suspect that through jail-breaking you could make an app yourself that could do it. Other than that, I doubt it's possible at all.