I see that both Telecom and Vodafone sell branded Nokia E75 phones.  However Vodafone wants about $300 more.

As far as I can see they are the same phone. In fact the 'Features' page on Dick Smiths site http://www.dse.co.nz/dse.shop/en/product/E1395
show this phone as WCDMA 900⁄1900⁄2100.  As 900 is the Vodafone 3G Extended frequency why isn't the XT phone 850/1900/2100???  (Apparently US version has these frequencies).

Surely this phone is more suitable for a Vodafone connection?

Can anybody tell me the downsides in buying an XT branded phone but using a Voda SIM?

Cheers