The majority of uni's/courses admissions tutors do NOT ring borderline students but make a decision based on their application so far.
Incoming phone calls are generally to confirm the decision to applicants that have missed a grade or in some cases will be used to offer a place on a less popular course.
I don't know of any dept in Soton that phones out on results day (including medicine) - we have 40-80 temporary staff manning a dedicated hotline to recieve calls and pass enquirers who've missed their offers and clearing applicants who've made the minimum entry standard on to the departments themselves.
If you do meet your offer please don't ring.
If you miss your offer by a grade then try checking on the UCAS tracker first - if your case was decided on by Wednesday afternoon then the decision will be showing on Thursday at 11AM when the tracker goes live.
If the tracker is still showing no decision *then* get in touch.
If the tracker is showing rejected AND you have a good reason for the uni to reconsider (an extra exam result not mentioned on UCAS, extenuating circumstances that you feel haven't been properly considered) then get in touch.
If the tracker shows rejected and the only reason you can present is "but I really want a place" I'm afraid ringing your firm choice is unlikely to make any difference (rejections during confirmation aren't made with spite - they're made because a department/uni simply *cannot* accept you...the reasons for which might have nothing to do with your application and everything to do with how well all of their other applicants did in their A levels)...your time would be better spent contacting your insurance and/or checking out clearing vacancies.
There are some excellent vacancies open during clearing and it's worth considering and looking into even if you have your heart set on a course/uni. Nothing in clearing is set in stone until you send off your CEF form so there is plenty of scope to look into things, visit unis and talk to academic staff about courses before you commit yourself to a place.
Best of luck to everyone involved