I tried all the above and nothing worked. I even sent it to a repair firm who changed the mic and the power button bizzarly - they then said the phone was unrepairable! I rang a guy I found on google - Mike on 01924 262112 and he sorted it within an hour. I cant remember what he said cured it but it wasn't software. I think his company is called iphone repairs direct - really helpful and I can ring my friends again - happy girl :)