Haha.. so, today I got a reply from Samsung Support and I have literally copy-pasted it here..
"Thank you for contacting Samsung.
I am sorry about the issue you are experiencing with your Samsung Galaxy S III handset since the JellyBean update and understand this can be frustrating.
We are currently developing a fix for this issue and we will be rolling it out via a firmware update in due course.
Iím sorry for any inconvenience that this may have caused.
If you require any further assistance, please contact Samsung again and we will be more than happy to help.
Online Support Team
SAMSUNG Customer Support Centre"
So that is some relief I should say. Eagerly waiting for that fix!! meanwhile to get temporary relief, it helps to clear up the ram every now and then before making calls or texts or zooming in on fotos to avoid the lag!
works for me..