I noticed that as well Jay about the seperate vent structures... but there are "hunners"! Something else Iv just realised I didnt mention is that before the roof structured was covered in that blue corrugated iron it was possible to see these vents running along the length of the north and south facades.
There are also a multitude of BT/exBT buildings in the Dial House vicinity let alone Glasgow (The Pinnacle, the one on Waterloo St that was just demolished (?), Telephone House, Westergate (hissssssss
), Alexander Bain). There are a few un-marked BT buildings still around so its quite possible that is a BT building in Renfield St.
Iv got an arial pic but dont know how to put it on properly
... Il ask Sharon!