tombrownzz: If it's 3g only then sometimes when you go into buildings, instead of falling back to 2g, the phone will not be able to find a network. Where are the 3g only cell sites in Tauranga?
That's because 2G *is not* a disaster recovery network. In theory 2G and 3G networks (on Vodafone) should provide continuous coverage, and overlap a bit.
It's this way because
a) Vodafone had 900 MHz and 2100 MHz use rights and at the time 3G was only available on 2100 MHz.
b) with so many 2G only handsets still in the market, moving their 2G 900 MHz sites to 3G 900 MHz sites would break mobile service to many users
People keep talking about "2G fallback" as it was a backup for 3G. IT IS NOT. Ideally the entire network would be 3G, like Telecom. This reduces maintenance costs, infrastructure costs, etc.