Update on my situation: I did not get lucky and had to pay for another refurbished iPhone4, just because of one function not working 'wi-fi greyed out'.
'New' phone seems to work well, I hope I never face this 'wi-fi' problem again; so annoying when you know you did not cause it and have to waste your energy, time on searching for information, nerves and money to deal with it.
Very much disappointed with Apple and its handling of problem.
ps. To all future defected iPhone users out there, who are at the moment surfing internet to find out a solution to their wi-fi greyed out problem, first of all good luck!!, but there is very little luck, you will most probably have to change your phone and pay for it!
Give feedback if you have time:
2) https://www.change.org/petitions/apple-to-get-apple-to-replace-all-units-affecte d-negatively-by-the-update-of-ios7-or-patch-an-update-that-will-remedy-the-issue s-many-loyal-customers-are-experiencing
3) https://www.change.org/petitions/apple-release-an-explanation-on-the-ongoing-iph one-wifi-problems
4) http://www.change.org/en-GB/petitions/timothy-d-cook-apple-ceo-fixed-greyed-out- wifi-issue
5) http://www.change.org/en-CA/petitions/replace-all-broken-iphone-s-caused-by-ios- 7-destroying-wifi-chip