Welcome to Vodafone Community
I have this problem too, or something similar, with a Galaxy S 16GB. I can make calls and use apps, all OK but when an incoming call rings neither the green (accept) or red (end) buttons respond to touch and the call eventually routes to voicemail, Maddening!
I have tried disabling wi-fi and bluetooth but fault persists.
Any ideas welcome or is it really a repair job as suggested?