IIRC it was Vodafone mobile that the company supplied in 1987 and started 083******. The battery was the size of 2 bricks with a telephone attached! The number stayed the same but as with all mobile numbers it latter had an 7 added to front so it became 0783 ******. Not sure the date that the "7" was added.Whilst I understand there is an element of hyperbole there, the first UK mobile call was made in 1985. The prefix for mobile numbers was also changed c. 2000, from 04 to 07x, so I doubt its exactly the same number
So that's approx 34yrs having the same number with the minor addition of a "7" in front as did all mobiles at that time.