Ah, if it's contracted out then that would explain Zen's reluctance to divulge the underlying number. About 20 years ago when I used to do things with huge banks of modems we used hunting groups to permit a single number to be used on many PSTN lines. These days, of course, there are no individual lines - it's a 2Mbit/s pipe (maybe even more) going into a multiplexer and probably software modems behind that. Or at least I think so - I escaped from the corporate telecoms world in 2000 to a life of retired bliss, a contented reject from the dot com melt down madness, so I'm a bit out of touch with modern stuff!
One thing I am quite sure of; I thoroughly dislike the trend to ever more 08xx numbers and the revenue distribution opacity that they create. Well, except for 0800 I suppose though even that is a pain in the wallet if you're calling them from anything other than a land line. Grumpy? Moi? 
John