600MHz
The 600MHz is regulator greed to sell licences. It's a band that makes no sense for unicast data. The range is too great and indeterminate for cell based concept of frequency reuse.
Even the 700MHz and 800MHz actually provides no extra broadband but just lets Mobile companies build less bases (with less capacity) than for 900MHz and 1800MHz.
Data / Unicast / voice of any kind, internet or not needs to be 900MHz to 2.6GHz parts of spectrum. Parts are already poorly uses due to regulators doing weak capacity and coverage demands in licences to raise auction prices.