Correct English Grammar

I have always enjoyed things English or British. Possibly because some of my relatives were from across the pond as they say. I was in England and Wales back in 1998 and had a great trip and enjoyed preaching there as well as seeing the sights.

My job is such where I am able while working to listen to a great deal of audio and I was coming up short many days where I did not have enough podcasts to listen to, so things got pretty quiet in my cubicle while I was working. In searching for other podcasts to download, I found the LBC 1152 website and the BBC website and each of them had some great podcasts.

During my listening, I have noticed a few things that I have always been curious about, maybe a reader from across the pond might be able to help me in my quest for the answers to these questions.

Whenever the British speak about a telephone number they always use the word "on" For example "call us on 001234" instead of what we say "call us at 001234" Why do they use on instead of at?

Wherever the British refer to someone being hospitalized they always say "in hospital". We always say "in the hospital" or "in a hospital" Again why do they do this?

I am not in any way attacking our British friends, just trying to gain an understanding as to why they say things a certain way.