In the early days of GSM the 900MHz band was the frequency of choice for many networks.
Then came the upstart entrants, Orange and One 2 One (T-Mobile) using the weaker 1800MHz band ensuring considerably more base stations were needed to provide equivalent coverage.
Flip to Australia and Telstra have recently deployed their HSPA network using the 850MHz operating over much longer distances, just as well, and so are closing their old CDMA service.
But now we have NMT crying foul that no one wants their CDMA 450MHz service. Unsurprising result as whilst technically better over longer distances, CDMA lacks the GSM handset pizzazz.