I thought all the networks were pushing for us all to use 3g (UMTS/WCDMA/CDMA2000) phones, with the idea of eventually using that to replace GSM. Why do we need a new spectrum band for technology on its way out?

So why did we switch to 1800Mhz again? The "better inside buildings" argument sounds familiar.

It's not a technology that's on it's way out, you can run 3g (UMTS/WCDMA/CDMA2000) on any frequency you want to.

The Manx telecom trial between 2100Mhz and 900 Mhz showed 900 wins all the time.

You can reuse loads of equipment.

The base stations give better coverage than 2100 so you can reuse the exisiting ones ( a good thing not just for saving money but also public opposition)

Coverage is 60% better, indoors is 30% and deep indoors 40% better.

This also means 10% speed increase and 5% overall capacity because it works more of the time so sending data only once.

In the U.S., Cingular uses an 850 MHz GSM band (vs 1900 MHz original US GSM standard frequency) in order to reuse existing analog equipment. It would be nice to have multiple frequency bands available and use them as needed, kind of like quad-band GSM today.

The reason for 1800MHz was for REDUCED range which allows the cells to be smaller and so give higher density of cells and higher capacity in urban areas. The idea is that by allowing use of 900MHz for 3g, in low density areas (ie in the forgotten world outside of the large towns and cities) it would give better coverage of larger areas - a double benefit of better coverage for the customers and less base stations required to provide it. Of course, being able to reuse some of your surplus 900MHz kit would be a bonus !

It would definitely improve coverage outside urban areas for 3GSM (3G), however, I wonder would it mean that 2G GSM coverage would be reduced.

In Ireland, like many EU countries, there's a mix of 900mhz and 1800mhz in use, they're not mutually exclusive. The networks use 900mhz as their core GSM frequency and 1800Mhz in densely populated areas to give extra capacity.

In the UK they seem to have been assigned exclusively to different operators.

In less densely populated areas, it's quite possible that 900Mhz would have enough capacity to support both GSM and 3GSM. I wouldn't like to see 'classic' GSM reception being damaged in urban areas though to promote a switchover to 3G !!