“A newlywed, who’s wife is pregnant and in labor, is he an exception?”
Leave it on vibrate.
“A Rabbi who needs to be available to answer sheilos, is he an exception?”
During davening? Someone from the back of the shul is going to call him up tell him he forgot yaleh veyavo and ask what to do?
“A mashgiach who must be available for kashrus reasons… is he an exception?”
During davening? What, the Rav must be available for the kiddush club during davening in case shailos come up?
“I can find many many exceptions”
All as silly as these?
“I still feel that those exceptional people should put their phones on vibrate mode,”
I am an exceptional person. I always turn my cell phone off, but maybe I will keep it on vibrate now.
“but I am firmly against the posting of ‘no cell phones allowed’ on shuls, and I feel it is against halacha.”
No cell phones, refer to their use, not that you cant bring one across the threshold.
“I know many Rabbanim who have cell phones in shul”
How many of those Rabbonim take phone calls during davening?
“and many shuls that have hard wired phones inside the Bais HaMedrash for people to use”
INSIDE the bais medrash? That I find hard to believe. Talking on the phone, whether during davening or while people are learning is distruptive, no matter how exceptional the person may be.